That saying Young made an ass out of Ali is a bit harsh (He certainly didn't make Ali look good, but Young did that to everyone) and I think the decision was debatable, Jimmy did merit a rematch.
As did Norton. Having Young and Norton square off in a title eliminator was about the only thing to do as both meritted another shot at the title (Norton more so IMO).
Ali handpicked Leon, Not because he was considered dangerous, but becuase he should have been an easy defense. He wasn't and Ali lost.
It's a bit disengenuous to state that Leon was more dangerous to Ali and give Ali credit for facing him twice.
The first go round NO ONE thought he was dangerous and LEON picked the rematch because lets be honest with our selves, Leon wanted NO PART of Norton who won a squeaker over Young.
Ali was not even IN a position to "pick" who he wanted next. He didn't GIVE Leon a rematch. Leon, now the champ, gave Ali the rematch.