1.why is cost irrelevant ?
2.I don't care if it's an AC in real life (i don't find killing machines aka weapons as fascinating as most people in this forum so i don't know anything detailed about this unit). INGAME it costs more than a t70 and as you said the t70 is a light tank so the puma should also be classified as a tank and not an armored car.
Cost is "irrelevant" in the sense that because a unit cause X MP and Y fuel you can´t expect it to perform better or not than other units of similar price. It gives you a different tool/opportunity of use.
I don´t mind if the PUMA is going to stay as it is. I just found it a bit counterintuitive for what it is, that´s all.
In my mind previously to use it several times, i expect it to be a support mobile AT which should had problems with heavier tanks. That´s not what i´m seeing. Maybe it´s penetration it´s bugged, time will tell.