It's not that is under priced but the problem lies in the indirect buff it got , let's start:
1 now can pen any axis rear armor
So can P4. Increase P4 price?
2 t34-76 mg buffed so t34 85 too
Isn't really that relevant, because its main cannon can actually hit infantry.
3 volks blob gone
Irrelevant. Pfaust and puppchen is just as lethal to it.
4 is in one of the best doc for all faction (motor guard)
Irrelevant. Arguably, its the only soviet relevant doctrine since forever.
Then has 800 hp and enough armor to make p4 bounce it
EZ8 got even more, yet it costs pretty much the same. Both, 34/85 and ez8 are half tier above P4, so them being stronger then it isn't really an argument. They got discount, because they are doctrinal units that require tech structure, no other vehicle does.
While having awesome rate of fire
Only panther and TDs shoot slower.
So it fits the meta too well
Not really an argument. It fits meta, because its reliable.
If you want to nerf units, because they fit meta, you'd have to nerf HMG42, all OKW inf call-ins, pretty much any unit that is reliable.
It still get easily beaten by stug and jp4