Teach does have a way of reaching people, and is charismatic in his own way, I agree with that
Tho Teach does gain a lot from Kuzan. Even if he doesn't use Kuzan's fruit for himself, he still had lots of crewmates without Devil Fruits at the time. To our knowledge, both Shiryu and Burgess didn't have fruits yet, maybe more didn't too.
Also, taking out a former admiral would give Teach lots of clout too