On different steam accounts, I tested this. If you think that one mg (240? mp) should be able to suppress 4 con squads (960 mp) and win the battle, then keep calling it OP. The four con squads did destroy the mg which killed the crew also.
However, 4 con squads against 2 lmg grens and 2 mg's (roughly equal mp and munis) also wasn't close. The mg's and grens wiped or suppressed all the cons easily, even without using rifle nades.
No, an HMG should not normally suppress 4 squads and win (if approached wisely), but what is not right/fair is the PTRS destroying the support weapons (such as mg in this case) with few shoots, and there is no question in that.
Also, that is a bad match up you exampled:2 hmgs+2 lmgs grens (if positioned correctly) vs 4 cons! of course they win!!! just because they are worth the same, doesn't mean the should be equal match up. this game is about countering units with the right unit. It is like I can't say a panzer 4 can (normally) beat SU85 just because they cost similar!
Any group of units (army) which cost the same as another should not be equal in match up, it all depends on choosing the right, cost effective units to counter the other unit.