To be fair though, the HVAP rounds give you about 3% better chance to penetrate a Panther/Brummbar than an equivalently vetted 6 pounder and about 6% compared to a ZiS. It's better, but overall not THAT much. Especially if you consider that a first shot might often be wasted during an enemy attack because the rounds are not popped yet and that without them you have a way way worse chance.
Again, at vet, the vanilla 57mm performs decently worse than other ATGs and about similar with HVAP rounds. Without vet, it performs worse without and better with HVAP.
You are comparing only penetration when M1 has other benefits over other ATG like:
33% Wider arc
28% faster weapon rotation
Higher speed
lower scatter angle
a second ability for extra range and sight.