They should atleast remove cooldown for the AP shells. Nothing worse then having it run out vs a heavy then being left with an AT gun that can't do shit. Maybe just a tad bit more base pen, but not much.
Way too many people don't make use of the AP shells enough though. I even see pro tourney players neglecting to use it.
Yeah, any problems with it are
entirely the AP shells. The rest is all good points, aside from the 4-man squad of which it has a vet ability that can reduce that flaw. The poor pen without the shells is justified by its low cost.
1.5X penetration (115/125/140 -> 172.5/187.5/210)
For comparison:
ZiS-3, 180/190/200
Pak 40, 190/200/210
Raketenwerfer, 180/190/200
6-Pounder, same as Pak 40
So it's reasonably within the same range of a Raketen's DPS for the duration though the 57mm's accuracy is worse (unless you're crazy enough to manage to put it at close-range to invalidate that and give it 10 more pen), slightly worse pen traded off with fire-rate. The fire-rate's higher enough that it's probably flat-out better than a ZiS-3 for the duration.