They're intentionally designed to pierce all obstacles and slam into their targets or near the target. This is probably due to the lack of BRACE and how easy PaK 43s are to kill (Very easy). Yes, intelligent placement can make it harder to kill the gun but its not like it can MOVE and shoot your face off outside its fire range.
Hill 400 is the Allied Arty players' dream map where the Axis base can be bombarded into rubble by SPG spam. No PaK 43 will last long there.
17 pounder cannot normally shoot through obstacles but they do have a piercing shot ability that temporarily can, like the Jagdtiger. 17 pounder can brace but is also a meme emplacement.
Easy counters: Any arty call-in. Skill Howie. IL-2zzzzzzzzzz. CalliOP. Any squad up close with a gun. Tanks up close and circle-kiting. And so on.
This. There is no brace mechanic for pak43 so it is intentionally designed to pierce all obstacles. Otherwise going pak43 will be braindead.