For different factions, units which have similar price do have different performance, for example, Ostwind and Centaur, Assault Grenadiers and Assault Engineers.
The axis variants you mentioned are known to be under performing (I mean so is the maxim). Different performance is fine, but the net should be comparable. The mg42 compared to the maxim is like conscripts compared to Obers, minus any utility.
Conscripts and grens perform relatively similar in the early stages of the game-both costing the same, but grens behind 80mp and 10 fuel. The maxim is behind literally double that and provides nothing of value unless massed. That is not good balance.
But even then, while underwhelming the ostwind and Ass grens can accomplish their goals. Ostwind will shoot up infantry and planes and ass grens are a solid open, they just fall off in scaling. There is no situation that the maxim performs to cost.