Its a bit different. As infantry you are tdaking into account the quality of training as associated with price andv to an extent even the name. Conscripts and guards both use nagant rifles. It's not unreasonable to assume thar the guards might shoot it faster and moyre accurately
There is a clear human element in infantry that id lacking in armour.
Well, there is a type of ammunition used as that kind of factor for vehicles if we want to be picky, which is easy explanation for range, penetration and AoE differences bewteen StuG and P4 for example.
Training is still a factor as sniper also uses mosin and shoots further then conscripts or guards.
Pretty much the only weapons that are consistent across the faction are the ones that are exclusively for one singular unit.
And since CoH is arcade RTS and not simulator like MoW, there is absolutely nothing wrong with inconsistencies as long as desired balance of the unit is achieved. What weapon looks like, who uses it or how its named couldn't be any less relevant here is balance is end goal.
Its not like elchino is wrong there.