Crew sizes are an inherent advantage of the Soviet faction. You've probably noticed you get 6 man crews if you recrew another faction's weapon. If you're willing to put in the manpower you could even gain 6-man Shock Troop MG 42's that can watch their own asses.
Correct, and they're rather too strong. Though you pay an extra premium on population on captured crew weapons, and you can't /build/ the MG42, you have to capture them.
I do think that these weapons shouldn't be balanced around their crew sizes though, if it's a factional trait. Soviet crew weapons should have the same crew size as other factions, or the number of crewmen should be tied to the weapon, not the faction crewing it. Either of these options would leave room for the Maxim to be buffed, and reduce the problems that soviet crews cause.