I just can´t see any situation where stormtroopers need g43 anything else than blobbing.
The commander is remnant of a time storms could get assualt rifles and the cheaper g43.
Also back in the days you could equip a shrek with g43 but not anymore, which you can with mp40.
It´s weird and need fixing.
Ok, your imagination(or lack there of) aside.
What if you wanted a ranger style or Heavier all rounder infantry, in those situation stormtroopers could need g43's. I mean the fact that they are not considered by you as elite infantry is just sad.
Also it's not a remnant feature of times past. Otherwise it would not receive buff's to it. It's seems that the mod team want's to encourage strom g43 usage. So a personnel increase the likes of fusilier squad would be quite good.
It's not weird that mp40 and shreck aren't exclusive. It's intentional and do not require fixing. Look at the patch notes when storms were changed.