The thing is that most tech are messed up and it is not simply a T-70 issue and I simply do not accept the argument that T-70 has to be "OP", it does not.
Have you considered the possibility that in context of other factions units compared to what opposition it faces, it is not op? If it was, it would receive rework akin to that of Stuart or 222.
One can delay 222/FHT by reintroducing 221
How reintroduction of weak unit will make people not go for strong one?
And I am not sure why in your opinion the T-70 should be a counter to PzII or FHT, Soviet have zis and where given PTRS to deal with these threats, if these option do not work there is something wrong in that design.
Do you know what FHT does to ptrs penals or you just drive straight into satchel range? Only AT rifle unit in game that can counter it are guards and only thanks to button, not PTRS.
Your solution of making T3 come with a previous building simply makes thing worse as even more powerful unit become available earlier. This is direction that should simply be stopped. When something does not work one should consider reverting back instead of continuing down the same path.
If you want to make a unit significantly weaker then it is currently, you need to allow it significantly faster and vice versa - that's the reason 222 does not cost 15 fuel anymore.
Also, what you want to revert about T-70?
It received only nerfs for couple of years straight, in fact it never received a singular lone buff, any buff it received always came with multiple nerfs, making overall performance lower then before the change.