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Then we will have to agree to disagree.
"The investment to tech is progress to more things so it can not all be placed on the T-70."
While that's is true, it's irrelevant during the early and midgame for high lvl 1v1
Mortar, maxim are not seen till late into the game. Zis gun is relevant in order to stall til the T70 against FHT or P2. M5 sees no use as a rush unit but late game to counter skillplanes. Su76 once u are so far behind that you will lose if you get your Zis circled around.
Unless you plan to skip T3, while using doctrinal units like Guards or Shocks, T2 see little play early on to make use of that tech investment because then your T3 units are gonna be arriving too late (this doesn't mean that some games doesn't revolve around light vehicles far into like 20 mins in).
Your plan is not to just touch the T70 cost down. For that to work you also have said that all 5 factions should had their light cars and tanks timing and performance touched as well as by your standard are too strong atm as well. IMO that's too naive to suggest thinking it can be implemented at all.