MBC Game StarLeague
These two tournaments pretty much always had the highest participation rates from the professionals around at the time, as well as being one of the most watched on television, having top end prize pools, and being recognized by KeSPA as some of the most prestigious individual leagues.
Some of the greatest Brood War players of all-time are often judged by their major performances, with NaDa and Flash winning six of them each, and iloveoov and Jaedong winning five each. sAviOr's greatest legacy, aside from his zerg-versus-terran meta-game revolution, is his accumulation of four major individual tournament triumphs over the course of his career.
Unfortunately, some of the older generation of greats, BoxeR in particular, are somewhat hard done by with this particular metric, since his peak years precedes the creation of the MBC Game StarLeague in 2002 (when it went by the name of KPGA Tournaments).
However, the history of competitive Brood War goes beyond the major individual tournaments, and there were numerous tournaments, some of which had its own qualification rounds, television channels dedicated to them, and overall prize pools that sometimes rivaled the likes provided by the much more prestigious Ongamenet StarLeague.
I will attempt to rank players by their non-major tournament careers, with the inclusion criteria for the tournaments being any offline individual tournaments that had double-digit number of registered professionals participating. Further more, if the details of the tournaments are totally unavailable, I will sadly have to exclude those tournaments because there are no ways for me to verify that over ten professionals competed in that tournament.
The reason for the threshold of the tournament requiring at least ten registered professionals competing in it was because there were too many invitationals in history that were mostly non-competitive in nature and had more of a showmatch feel to it.
I will not include tournaments such as Sonic StarLeague or AfreecaTV StarLeague since these tournaments were created after the end of professional Brood War, when the vast majority of ex-professionals had moved on to other fields.
So without further ado, here are the players who had great success in non-major tournaments that had over ten professionals participating in it, ranked by the sum total cumulative number of the professional participation of all their non-major triumphs.
All these players had triple digit number of professionals participating in their successful non-major triumphs.
Champion of 2007 Seoul International e-Sports Festival: 194 professionals participating
Champion of GomTV Classic S1: 147 professionals participating
Champion of WCG 2008 Korea: 24 professionals participating
Champion of WCG 2010 Korea: 24 professionals participating
Sum total of participating professionals from all triumphs: 389
Comments: Jaedong benefits greatly from winning two colossal tournaments in terms of scale, namely the 2007 Seoul International e-Sports Festival, and GomTV Classic S1, both of which had over 140 professionals participating in it. He is also the only two-time champion of WCG Korea, which was changed into an invitational-sort tournament for top ranked KeSPA players at the time (as opposed to the past when it was more of an open tournament).
Champion of PSBmegapass Cyber Game Grand Prix: 17 professionals participating
Champion of 1st GameBugs Battle: 16 professionals participating
Champion of 2001 iTV Newcomers: 12 professionals participating
Champion of WCG 2002 Korea: 67 professionals participating
Champion of 2002-2003 KTEC KPGA Winners Championship: 10 professionals participating
Champion of GhemTV FindAll Challenger Open Starleague: 72 professionals participating (qualification stage included)
Champion of 5th iTV Ranking League: 99 professionals particpating (qualification stage included)
Sum total of participating professionals from all the triumphs: 293
Comments: YellOw's moniker was the "King of Special Events" for a good reason. YellOw was sickeningly prolific in small scale invitationals and less prestigious open tournaments with qualification stages that later died out due to financial struggles. Korean communities said that it was easy to distinguish which tournaments were major tournaments, and which were non-major tournaments, because YellOw would come second in all the major tournaments, and win all the non-major tournaments, often versus the very same opponents who denied him the ultimate glory in those major tournaments.
Champion of 1st Game-Q World Championship: 16 professionals participating
Champion of 2001 KPGA September Tournament: 56 professionals participating
Champion of 2nd GhemTV StarLeague: 82 professionals participating
Champion of WCG 2003 Korea: 98 (perhaps inaccurate) professionals participating
Sum total of participating professionals from all the triumphs: 252
Comments: H.O.T-Forever was an old school zerg player whose entire tournament career precedes detailed written records on databases such as TLPD. For example, from the word of mouth, it seemed that for SBS Progamer Korea Open King of Kings, for example, there were literally hundreds of professional gamers who participated, but none of the records of it remain. However, H.O.T-Forever was the greatest zerg player from Korea before YellOw had his ascension to the top of the ladder, and had numerous tournament success in his time, although the vast majority of his success isn't celebrated to this date.
Champion of 3rd iTV Ranking League: 35 professionals participating (qualification stage included)
Champion of 4th iTV Ranking League: 67 professionals participating (qualification stage included)
Champion of 3rd GhemTV StarLeague: 100 professionals participating (qualification stage included)
Champion of KT-KTF 2003-2004 Premier League: 20 professionals participating
Champion of Shinhan Masters: 11 professionals participating (Pre-Masters included)
Sum total of participating professionals from all the triumphs: 233
Comments: NaDa has won almost everything there is to win during his time as a professional, but interestingly enough, never had much luck in WCG Korea, which resulted in arguably the most accomplished professional Brood War player of all-time failing to qualify for any of the WCG main stages.
Champion of GomTV Classic S2: 176 professionals participating
Champion of WCG 2009 Korea: 24 professionals participating
Sum total of participating professionals from all the triumphs: 200
Comments: Bisu was not only the most decorated protoss player in the major individual leagues, he also happened to have great success outside of it, his greatest non-major triumph being GomTV Classic S2, which was the largest in scale out of all the GomTV Classics (in terms of player participation, because teams like SK Telecom T1 didn't allow their players to compete in the other GomTV Classics).
Champion of 7th iTV Ranking League: 105 professionals participating (qualification stage included)
Champion of KT-KTF 2004-2005 Premier League: 51 professionals participating (qualification stage included)
Sum total of participating professionals from all the triumphs: 156
Comments: July, during the earliest stages of his career was monstrous in any tournaments he happened to enter, and won two fairly large scale tournaments, both of which had an open qualification of sorts.
Champion of GomTV Invitational: 16 professionals participating
Champion of GomTV Classic S3: 123 professionals participating
Sum total of participating professionals from all triumphs: 139
Comments: Flash competed in an era when all the non-major tournaments were starting to fade away, with basically only WCG Korea and GomTV Classics being the main sources of non-major tournament glory. While Flash never had much success in WCG Korea, outside of his second place finish in 2010, he was incredibly successful in tournaments hosted by GomTV.
Champion of 1st PgR21.com Tournament: 16 professionals participating
Champion of WCG 2005 Korea: 101 professionals participating
Sum total of participating professionals from all the triumphs: 117
Comments: XellOs was a beastly terran gamer whose legacy is somewhat hard done by if you limit the frame to major tournaments only. XellOs was one of the few players to represent Korea multiple times in WCG main stages, and won what was probably (if my calculations are correct) the most stacked WCG qualification rounds all time.
Champion of ZZGame.com Invitational: 29 professionals participating
Champion of 3rd Game-Q StarLeague: 16 professionals participating
Champion of WCG Korea 2001: 66 professionals participating
Sum total of participating professionals from all the triumphs: 111
Comments: BoxeR's records in tournaments from 1999 to 2000 are not well recorded, but his stellar tournament performances in 2001 are well documented. During his peak year of 2001, BoxeR was winning a large share of the large tournaments he entered, raking in prize money like no other player of that era.
Champion of 2000 Kamex e-Sports Championship: 34 professionals participating
Champion of 2001 iTV All-Star 8 Exhibition: 10 professionals participating
Champion of 2001 KBK Jeju International Game Festival: 64 professionals participating
Sum total of participating professionals from all the triumphs: 108
Comments: TheMarine was an old school terran player whose past tournament record, especially ones hosted by KBK, are not fully chronicled. However, he wasn't the 2nd ranked KeSPA player for 10 consecutive months without a good reason. TheMarine was a decorated rival of BoxeR's, who tended to excel in short offline tournaments held over a couple of days, instead of the more extensive televised leagues that was filmed over a couple of months. He was supremely gifted in terms of sound orthodox play, but struggled to replicate his short tournament form for televised matches.
While it is extremely difficult to accurately assess the competitive results of various players in non-major tournaments, I thought that one way to measure it would be the cumulative player participation count, instead of ranking it by prize money earned, since prize pool varied greatly depending on the era, and because hyped up one-versus-one showmatches like SuperFight, or GomTV Classic Special Match often had superior prize pools to actually competitive tournaments with greater number of high calibre players.
This ranking would partly explain why old school players such as H.O.T-Forever and TheMarine are viewed in such high regard, despite not having the greatest accolades in major individual leagues. There's more to TheMarine than a player who reached two semi-finals within the major individual leagues, but his entire career narrative isn't captured by major individual leagues alone. For the more modern day players, the ProLeague provided another platform to prove a player's competitive worth, but TheMarine played in an era where his merit could be proved elsewhere, but many people tend to only recognize his major tournament performances.
There has been a lot of tournaments that happened after the professional scene had been extinguished, but I thought it would be best to separate the results from these two scenes (professional and streaming scene), since there are obviously confounding factors, such as the timing of the retirement from Starcraft 2 heavily influencing the number of tournaments a player could attend for the streaming era of Brood War.
This ranking also contains a pretty comprehensive list of all the non-major tournaments that had heavy participation from most of the professional players. There weren't a lot of non-major tournaments that had triple digit numbers of professional gamers participating throughout all of history. 3rd GhemTV StarLeague, 7th iTV Ranking League, WCG 2005 Korea, Seoul e-Sports Festival, and all three GomTV Classics were the rare exceptions that had a large enough scale to include over 100 registered professionals competing within it.