Why doesn't zerg downtech?
I mean, in late-game macro situations the zerg has lots of larva, lots of money, and lots of bases to tech switch but almost every zerg I see at all levels sticks to the highest tech they have access to (BL/infestor, roach-hydra, etc). Almost all of those zergs will end up complaining that they cannot "Break" certain unit compositions (including terran ghost+tank pre-patch).
In the specific case of the Terran MMMTGV late-game unit composition, zerg should know they can remax much faster if they do damage to Terran tech units (tanks, ghosts less so, vikings) and can continually work down the terran army with wave-after-wave of ling/bling or switch some gas into mutalisks to harass reinforcement lines or worker lines, etc.
Upon watching a game of ASUS ROG (Strelok v Bly G2), Bly goes Infestor Ultra (with a bait of infestor broodlord) with well upgraded lings. Strelok is going MMM+T with some vikings from the baited greater spire tech, but is able to continually wear down his opponent. He loses several major engages with good fungals and gets a much later 4th than he wants. Instead of continuing an assault with ling/bling (low build time and fairly cheap compared to other remaxes) he decides to try and make BLs even though there are some vikings on the field. Mutas or ling bane could have done wonders vs this Terran...
So I'd like to hear the issues with downteching your army composition temporarily while, say, expanding, banking gas to use for the next big round of tech units, or w/e.