It is quite pointless just to compare flat penetration values of two units from different factions because average armor values those units got to face is different for those factions.
A StuG III is less likely to pen an IS2 than an SU-76 a King Tiger. A tad interesting that.
Though 140 armor still isn't really that thin for 80 long range pen of allied meds.
Since when does anyone sit in front of a StuG III to shoot at it's frontal armor unless they are using an AT gun or TD with superior range? Yes the StuG III can technically bounce frontal shots from the weakest cheapest mediums in the game but that's not a very ringing endorsement.