Frazier clearly has the advantage in terms of power and, most likely, durability. Leon, on the other hand, may be speedier and have the same stamina as Joe. Leon was a speedier starter than Joe, which could be troublesome early on given Leon's power. Leon could also maintain that pace and stick with Joe for an extended period of time. I'm going with Joe by SD, although this may even be drawn. How About You Guys?
Don't see any way that Frazier doesn't fold him like a faulty wheelchair. Qawi was a far smaller version of a lesser Frazier, and he knocked Leon silly.
Frazier only loses to Ali (and not always) and Foreman; not by Leon Spinks. Frazier wins by knockout, and early in style.
Frazier blasts him out into yee-haw. Easily within the first three minutes. And yeah, I'm keeping in mind Joe was a notorious slow starter. Leon fought coming forward. As Holmes stated (in reference to Iron Mike): "Joe loved guys like that. He didn't have to chase them down".
Prime vs. prime, this is an early blowout win for Frazier. Make this bout on Feb. 15, 1978, with Frazier replacing Ali against Spinks, and that might have been interesting.
Much like Foreman-L. Spinks, this matchup has really never occurred to me. Leon, in whatever version you would consider his prime, has absolutely nothing to keep Joe off of him. Joe stops him inside of six rounds and if he catches Neon Leon early, it ends right then.