Some people are being a bit too rigid with the comps presented. MTM can be done in several ways: starting bio and getting tanks late game, or earlier, or go for a 1-1-1 and get tanks early enough. MTM can perfectly keep up with upgrades and mobility with bio, and fare better, because pure rine > rine rauder, and IMHO, a relatively small tank force is actually quite helpful in this case. Why? Because you don't need a big number of tanks to get an advantage in straight up fights against bio, it still forces a decent number of marauders and it keeps your army mobile enough. The tank:rine:Medivac ratio? I think it depends on the situation.
Then again, I'm just plat, so take some of this with a grain of salt.