>joins MM1 development half way through
>all the design plans have already been created, alongside the story
>Rock, Roll, Wiley, and others have already been designed
>he is tasked with redesigning Elec Man and Bomb Man
>"I am the creator of mega man"

How does one come to this conclusion?

Capcom rewrote history to claim he was the creator because anyone who could actually claim to be the creator left after the first game. He got overpromoted simply for being on the team for mm1 and then continuing to work there. No idea if the conman believes his own hype or just repeats it because it makes him look good.