Two key differences.
1) Gerrard wanted to play midfield B2B and he's fairly good at it, while Pogba only want to attack playing further up the field, on the wing or centrally and he's usually better there than at deeper positions. I remember it's because the Pool manager at that time (Rafa was it?) wanted to instill a tactical system, with disciplined holding midfielder. Gerrard is just not good for that specific role, so the next best position for him is RM or SS/CAM, best at RM so they still get to use his energy, B2B abilities, and long passes. Us instead insist on forcing/shoehorning Pogba into a role where he just doesn't fit, seriously the only useful thing Pogba had is his long passes for CDM role, which is not enough since it's not like Pirlo-esque nor Scholes-esque (not even Carrick/XabiAlonso-esque) and in return our defense are far more exposed, not worth it.
2) Gerrard is far consistent and step up more often than not, like a leader. Pogba doesn't and we can't iron out his usual poor decisions makings at the back and inconsistencies.
Damn it, hate this thread, forces us to basically praises Gerrard.