The weapon might be better but it not available at all squad member so the moving DPS of squad can be comparable even if the G43 is superior.
Moving DPS of a full Panzerfusiliers squad is ~23 at close range (10) down to ~8,5 at max range. G43 Panzergrenaiders have at least ~32,2 and ~10,5 (probably a bit higher because of the latest buffs).
Hell, even cheap Grenadiers have ~18 and ~6,3.
Compared to Penals that have ~14,3 and ~6,3, that is a significant advantage. Especially considering DPS is consolidated in the G43s down to the last two-three models, while Penals straight up lose 17% DPS with every model drop. Only Paratrooper and Ranger elite carbines have comparable total DPS, purely because of raw strength by numbers. But they are elite squads, suffer from the same straight DPS per model drop loss as Penals, and they lose it as soon as they get their weapons upgrades.
TLDR the G43's high moving DPS is a unique and deliberate trait, and no other weapon or more specifically weapons upgrade is really comparable. Some weapons come close, namely elite Carbines and Guards Mosin, but the comparison for those is artificial at best as elite Carbines are replaced by mandatory weapons upgrades, and upgraded Guards only have two Mosin rifles, and both are the first weapons to drop when the squad loses models.