Would he have been fighting at 48 years old and confounding young champions and contenders with ring savy and experience like Bernard Hopkins is doing today?
A better question is, if not for Parkinsons, would he ever have lost the title to Spinks? Then again, it would likely always be something. Too many ring wars with Norton, Frazier, Shavers and Foreman.
His career would still have been over by the time he got to 40 years of age. His losing fight against Larry Holmes would have been more competitive,but he was far too long in the tooth to have beaten him at that point. He may well have had enough left to outscore Trevor Berbick,but would have lost to some other top fighter.
Ali didn't 'get' Parkinson's. He developed it. If longevity is the only mark of greatness, then Bernard Hopkins was/is greater than Ali and many, many others. A bit of a two dimensional attitude though.
Thats crazy looking at your avatar how small mike is. Its almost like he was in a catch with his size. Just slightly too big for cruiser an a tiny framed heavy.
Length =/= size. Tommy Hearns is smaller than David Tua even with Tommy being 2 inches taller. I think Tommy/Tua is a very good example why length=/= size. And Dwigth Muhammad Qawi wasn't a featherweight either. Tyson was natural at 215, very stocky built, very big. Being short and stocky can be an advantage depending how you use your physical size, and Tyson used it incredibly well.
Ali may well have done what Larry Holmes did. Being carefully matched and having a 'Ray Mercer' type victory over a young,strong but limited top contender.