It is more like you give up a lot of close to mid range DPS to gain a okay to decent DPS increase to long range and okay to very good when moving.
Eh, depends how you want to look at it.
6 DPS for any other infantry is quite a lot, but for PGs that's ~10% of their close range dps, but more with range increase, but that is compensated by really incomparably higher on the move DPS especially at longer ranges, so unless you constantly fight on ranges below 20-25 and never have to move in or move at all, g43 outperforms stgs.
If you want to ram rifles into opponent and use it from very close range and approach under cover of smoke or los blockers, stgs will be better.
I'd say it is a side grade for sure, but it is not a clear upgrade as you say. Overall the upgrade a weird design for PGrens when looking at the additional abilities
I've also said its a side grade, but to me, as I have said, what you give up is well worth it vs what you gain, given more mobile nature of PGs, where they utilize g43 form most.