It is an interesting debate over a few brews - yes, it certainly is.
Ali was a great fighter, no doubt about that - he had a great chin, fast hands, was mobile and had uncanny reflexes.
But he was nowhere as consistent as Joe Louis - that's just a simple fact.
And, TBH, my favorite fighter, Joe Frazier, beat a prime Ali in 1971.
I also feel that Ali had a lot of syrup ladled on him, as it were, because he had the title taken from him in 1967 and was punch-drunk in his later years and people felt sorry for him. Most, if not all, boxing experts from the late 70s onward spared objective analysis of Ali's boxing abilities because Ali took too many punches and developed Parkinson's Syndrome.
I think you're trying to measure heavyweight boxers' greatness the way we measure 100m sprinters' greatness, and you just can't do that. Usain Bolt is the best 100m sprinter of all time because he ran 9.59 secs.
With hw fighters, it ain't so simple.
The heavyweight division was relatively small in Joe Louis's day. It got bigger in Ali's day … and it's even bigger today.
Tyson Fury is a current hw champ. He stands at 6 feet 9 inches, has a reach of 85 inches, and weighs 256-272 lbs. Does that make him a great fighter? IMO, I don't think it does.