It highly depends on G43s and STGs. I would not call Pgren STG worse then elite G43, they are just different. Probably same could be said about basic G43s and Volk STGs. But if you compare elite G43 with basic STG, then you are probably right.
That depends on your definition of better though. In case of PG's, units that can't win against them at close range still does not with g43 upgrade the same is true for units that beat them at close range. How ever unit that could beat vanilla PG's from long no longer can beat them from long when they have G43. Also G43's are much better at running and gunning. So g43 for PG's are a net win over all. The sam can be said for Stormtroopers. As even Cav rifles can beat them at close range. What changes for them is their Time to kill support weapon.