If the 7man cons upgrade is somewhat difficult to place in the soviet tech tree, is there some reason it couldn't be split into multiple "levelled" upgrades, and spread out a little more across the tech tree?
Ergo, after tier 3 you can allow Cons to upgrade to 7 men (or allow them to upgrade to have the reduced reinforcement cost) and then after tier four is constructed apply the remaining part of the upgrade (either behind a further research or immediately upon construction of tier 4)? That might help alleviate how spiky the upgrade is, while still allowing Conscripts (and Penals) to be improved somewhat in the midgame.
Perhaps there is something I'm missing?
It already too powerful. 7 men conscripts costing 258/60 will beat 5 men grenadier costing 270/60 while taking up a ability slot. It should be toned down move to T3 and be done with it.