I don't really understand why an occasional bounce from a p4 is so unbalanced. When it comes to regular tank battles, other tanks bounce shots off the p4. I've had a p4 miss, but not bounce on an allied tank. When it comes to unfair bouncing it only gets worse as you go up from p4. Axis heavier armor can double or triple their already high health with bounced shots. 57mm, m36, m4, bazooka, all frequently bounce. Axis AT can reliably 4 shot an m36, with p4 sometimes needing 5 on m36. At least with USF, I've had panthers just parked in front of a 57mm, not pay attention to the panther, bounce 4 57mm shots, then notice and move it back. The m36 still has disappearing rounds too, either it doesn't shoot out the barrel or the round disappears when it reaches the target, doing 0 damage. It's quite pathetic, so I really don't see why the p4 sometimes bouncing one shot is anything significant.
Every AT-gun/tank/whatever has disappearing rounds. It happens on all sides. Nothing limited to the M36.
The odds of a Panther bouncing 4 57mm shots in a row are 10% and that is if all shots hit front armour. And that is for a vet 0 M1 ATG without HVAP.