One thing has always bothered me about Perospero surviving the fall:
He seems absurdly confident about waltzing into allegedly enemy territory (according to him) by himself. He directly references that
"We'll deal with you" and that the
"Big Mom Pirates will reign supreme".
I really do believe he has something up his sleeve with his crew, the odd relevance of him being here and not others who are stronger than him (apparently at least Snack and Smoothie) is weird to me. Unless they ARE here.
Its been a popular theory Pero is carrying one of Mont-d'Or's books, which has the Mama Canter inside.
I feel like that is 100% an Oda thing to do, to basically shift up the battlefield by literally dropping the BMP right in the middle of it, causing even more chaos to an already chaotic arc. It also entirely opens the potential for more allies arriving, namely Sword or the Whitebeard Pirates.
I REALLY do think he's there to serve a purpose, such as bringing the BMP onto Onigashima.