i too think the su-85 has a bit too much going for it and greatly overshadows the su76 as a result much in the same way that the jackson makes like 193 different units pointless for the USF.
i actually agree with all the suggested changes in the OP, which is rare frankly...
the su85 shouldnt be your go to TD but instead the one you bring out when its needed for heavy armour. good in all situation TDs are bad design and since the soviet actually have 2 TDs its unacceptable (at the very least the jackson has the benefit of being the only dedicated TD stock)
some chages however id like to see, or at least discuss for both SU TDs would be looking at their vet
for the su76, vet 1 imo should be changed to augment the barrage. cooldown, cost or even firepower instead of the infantry tracking so that keeping one around even when you need your su85 is rewarded well.
additionally id like to see a rework for focused sight so that its not so much of a free boon (yess, it does reduce mobility and what not but given the reliability of the su85s gun, especially with vet... well frankly it shouldnt self spot for free)
what i suggest instead is a timed ability, with a munitions cost, that functions like the USF AT gun range boost. due to the su85s design its unable to chase and generally is defensive, so id suggest replacing both focus sight as a passive and tracking as a vet 1 ability with a combination of forward sight and take aim, giving it the ability to take that extra shot, at the cost of munitions and vulnerability making ti more of a tactical ability you need to time than something you only turn off when you need to flee. giving it say 15 seconds of self spotting and increased range (+10?) for 30 mu and a 30 or more second debuff makes it good to help secure a kill but vulnerable to counter attack
anyways thats my addition to the discussion. but if only the OP was applied i would accept that change as well.
I agree with this it is bad design and is a common trend with soviet and brit units . Having a unit that is amazing at everything with no real weakness is just a terrible idea look at the SU 152 for example . Why should it have amazing armour , amazing AI AND amazing AT AND Amazing range AND Amazing damage.
Look at the elephant in comparison .. only amazing at and range with clear weaknesses.