ST44 upgrade is a badly designed upgrade (Similar to Penal SVT) concentrating the DPS of large squad i into 2 weapons while having a almost linear curve reducing the effect of relative positioning. In addition is allot closer to the G43 (which uses the carbine profile) then to other ST44.
It also part of the reason why most other weapons where buffed.
By replacing the ST44 upgrade with MP-40 upgrade a player would simply have to choose which of his units he wants to upgrade with MP-40 and which leave with K98. Then Ostheer/UKF would not be in desperate need for buffs and one could start nerfing the Soviet and USF.
By that logic we'd have to junk any and every upgrade that concentrates DPS into 2 members, and as a continuation of that logic, also one member. Same problem of having too much DPS concentration. Shall we also have the Ober LMG34 nerfed to oblivion because it has 3.77 Ober Kar 98s worth of DPS at 35 range? Ostruppen (Grenadier) LMG nerfed because it has 8.37 Ost Kar98s worth of DPS at 35 range?
I think the existing system works fine. The whole point of the original StG44 volks upgrade was to give them better AI performance as I can tell you even the old old vet V volks really struggled 1v1 vs an LMG inf squad. Reducing it to Kar 98s would make them seriously overwhelmed in late-game even with Vet. As it stands, yesterday I had exactly this situation of a vet V StGvolks vs (vet III?) M1919A6 Rifles. BARELY matched that firepower. Barely. Only cos he was in open and I was in Light cover, did it become a win for my squad.