I know, but still, I think Relic's logic here is it's called an assault gun, thus it's an assault gun.
Ironically there is nothing to assault. The Soviets have no hard points or bunkers and they can't take down buildings faster than any other big barreled unit. Though they have better MG42s and HEAT shells they explode really fast if you try to assault a combined force of mgs and AT-guns because those will hurt them badly which means that they can't project their firepower on the MGs and conscripts guarding the AT-gun. So. If there is nothing to challenge them or there is a screen of other tanks maybe then they can perform better I might think.
The Puma is great. It's gun is powerful, ideal for flanking big tanks. They die as quickly as a scout car which makes them cost/effective only in the right hands.