Imo Squad should be separated into categories and have slot weapon receive bonuses or penalties accordingly.
I like the Men of War system where every unit has a set of stats for how well they handle a weapon.
For example, a "border militia" russian soldier (first tier infantry) has a "1" in accuracy to all weapons besides the one he's equipped with, the rifle, which is "2" (the number is a flat modifier to accuracy so it doesn't exactly translate but you get the idea)
Whereas the elite Marines troops have a "4" in accuracy to weapons besides the one they're trained on, which would be "5".
How could this be applied to CoH3? Weapon profiles could be slightly modified by a similar accuracy number. Say, riflemen are t1 infantry for example, and since something like panzergrenadiers come later maybe they are t2 infantry so they get a higher number.
EDITED: So basically it's the exact same weapon profile but with an increase to accuracy based on what "tier" of infantry it is and also how familiar they are with that style of weapon.
I.E. Shocktroops would probably be more accurate with an MP40 they picked up off the ground than Panserfusiliers would be, because Panzerfusiliers train with rifles and Shocktroops with SMGs. (This is just a hypothetical where panzerfusiliers and shocktroops have the same tier. Obviously this isn't true in game.)