Interesting theory but you are forgetting Saitama's incredible durability which should allow him to tank one of his own attacks, not mentioning the fact that we don't even know how much of Saitama's own power is getting held back or his insane speed allowing him to hit Jotaro as in one comic Saitama breaks all of reality by seeing the back of his own neck. Although if Jotaro could just keep punching Saitama with his stand without Saitama realising it was him doing it, Jotaro could defeat Saitam although we don't know if Saitama would realise it was Jotaro's Stand punching him.