I can't be the only one who was almost certain from the beginning that Jinbei wouldn't be going back with them, right? It really felt like Jinbei was in this arc because he happened to have business with Big Mom and Luffy happened to be there. I can't put my finger on why it would be weird to recruit a crewmember when only half of the crew was present but it just is to me. The timing was just never right to me.
Jimbei already joined back in FI, he just needed to handle the situation with Big Mom first. It's like when Nami didn't join right away but it was a foregone conclusion. The whole crew was assembled at FI so him coming back now, with only half the crew, didn't really matter since everyone knew it was just a matter of time before he came back. I don't see why there would have been any certainty that he wouldn't be going back with them since Big Mom was the only reason he needed to delay it and they were poised to have resolved that conflict right now. Oda just took a bad narrative turn here and is flubbing the ending to this arc like a mofo so this whole thing with Jimbei isn't the only crappy outcome we have to put up with.