I don't think I can agree with your opinion. Puma does see more action but imo that has to do with the fact that it is needed to counter allied light vehicles. Su-76 is not needed and going T4 is simply more rewarding.
I also doubt that Puma in more cost efficient than Su-76 vs mediums and above. I suggest you calculate the changes to hit and penetrate for Puma and Su-76 vs mediums (or even heavy) because Puma's stat are rather bad at max range.
Puma does have better vision but SU-76 has the extra utility of barrage.
In sort I doubt many people would bother building Pumas if the opponent had not build LV.
Yes I rarely see the puma being used vs soviets. Vs usf and ukf it makes sense that is does see more action as their lv timing is earlier and lasts longer then soviets mostly. Again imo soviet lights come to the party to late.
This is the problem imo. why does the faction with no stock ai upgrades get their lv's so late? While all other factions with ai upgrades get their lights earlier?
Vs soviets flak or flametrack is usualy better then a puma as their is no lv close to being build to counter the former. Just zis and ptrs wich they easely get away from or play around, only the clown car with ptrs but that usualy a suicide move and t1 is neccesary.
Also i never meant to say the puma is more effevtive soley vs mediums then the su76. I said the puma has more chance/use throughout the game. The vision of the puma is a big passive free perk, it smoke also can help more then one unit in a pinch. The su76 barrage while usefull makes the su76 vunerable at the same time.
Yes the puma has 50/50 chance to pen a allied med at max range. The su76 70/75ish percent chance to do the same vs okw p4.