The problem with that logic is that the Maxim and M2 still work pretty well in buildings, while the MG 34 and MG 42 do not.
Thats design decision.
Switching sides is is dependent on reload speed.
Maxims are useful in buildings, while MG42/34 are not, but there is nothing wrong with it really.
LMG grens are exponentially more viable in buildings then conscripts as well, but you don't see people complaining about it all the time.
Some units have advantages over others in given circumstances, its asymmetrical balance at its finest here and as I've said already, its not like axis doesn't have units that get the advantage in garrisons over allied infantry.