So as you can see currently different mag means it’s a different weapon. In my opinion change of type of magazine should be a side grade.
You could mount drum mag but it would cause longer ads and reload time and less total ammo.
You may argue that for example PPD needed conversion to fit drum mag, but it’s conversion, not different weapon.
There is also abomination named “MG34 with patronentrommel” as separate weapon from MG34. To mount this magazine you didn’t even have to do conversion, you only had to change feed cover.
(I remember it from some screanshots from twitch but I may forgot the details. If you have screenshots I’m talking about that please place it in comment.)
Of course current situation is the result of weapon upgrade system and probably also monetisation system.