I have read the next balance patch notes and I lol...
Relic says they want to increase the viability of light vehicle combat. So the T70/M5/SU76 will come out earlier than before by 40 fuel. And they increases OSTHEER Building 3 and Building 4 fuel cost(Stug and Pz4 will be late), then decreases USF T3 building cost(quick STUAT).
So the first T70 needs only 50+80+75-50=155 fuel cost the next patch. (Don't forget 50 fuel is given to soviet at the starting of the game.)
The first STUAT needs only 60+80-40=100 fuel. (Dont't forget 40 fuel is given at the starting.)
This is the problem with reading and not playing the patch.
USF starting fuel is 15.
The cost for the stuart is 70 not 80.
Adding up to 130-15=115
Your argument completely ignores any upgrades. For USF nades are increasingly important to deal with mgs and soviets will almost always need to tech at nades. I haven't played the patch enough to say if it is possible to stall the upgrade until after the first light vehicle but I'd assume that you can if you go guards.
Against Ostheer Lieutenant seems to be the favourite choice for usf because it gives you some way of trying to deal with a sniper quickly, but again, it's too early to tell how the change to the captain cost will influence things because I haven't played enough.
Ost might struggle against light vehciles but you forget that the early game will change due to the mg42 change, the 221/222 comes out at a time where it has a good window of opportunity and light tanks will delay the tanks for allies, which might lead to an interesting dynamic of pushing back Axis when the light tanks hit and then being pushed back again when the first medium tanks hit.
I don't see the problem as much in the t70 or stuart but in the m5 ht, which is very strong with the aa upgrade since the last patch and will hit rather early and won't delay further tech or vehicles as much. Then again, the Soviets do not have a generalist tank in t3 anymore giving ost mediums more room to operate.