Would have lost to a numbers contenders who would have turned his electricity out long before Ali would have got hold of him.
Willard’s biggest problem after the Johnson fight wasn’t just his age, but instead his lack of motivation. Lack of motivation after achieving success is often one of hardest obstacles to overcome. Even Ali after becoming champion strated struggling with getting motivated to keep fighting. This was especially true when Ali regained the title against Foreman. So even if Willard stopped aging after beating Johnson He’d still get bored with boxing after a couple more paydays, so Willard would quit boxing long before an Ali fight could ever happen.
The smartest man wins more often then not. I think, though they may not look "intelligent" in the ring. Who could be more intelligent then a man with 50 years of experience and no psychical clock? Might be an immortal develops his own ways, might be he tries all manner of things and learns exactly how to fight everyone. His bodily gifts never held him back, legendary stamina truly. He'd wash Ali with ease when you give it some thought.
A better matchup might be Jimmy Ellis or James Quick Tillis. Any version of Ali before the Spinx loss toys with Willard. I would pick the Ali of the Wepner fight to pitch a shutout.
Ageless Willard destroys all!! No. Only kidding. Ali up to his very last years finds a way to beat him. By the Spinks fight maybe Jess could get a decision. Mauls him around. He'd lose the rematch tho!
Impossible question to answer. If he stuck with his style he's have had innumerable beatings by the time he faced Ali. On the other hand if he consistently learned as time went by he might be a kind of Wlad Klitschko with an iron chin and he'd wipe the floor with Ali. All I can say for certain is Willard as we saw him against JJ would have gotten shellacked by Ali no matter how many rounds you make it.
Is this question also meant to be viewed as an to attempt to estimate how much boxing has advanced - invoking an ageless and physically self repairing Jess “The Thought Experiment Guinea Pig” Willard, who will be well drilled and updated mentally and physically in accord with those advancements - in order to reflect the associated advantages? Are prior boxing “practices” of any worth as “experience” if they have been allegedly (as some may believe) superseded by newer and improved methods? There’s also the potential problem of Jess having to unlearn and then relearn - (the old dog new tricks syndrome) - instead of just being born into and availing himself of the most ideal techno world of boxing - in terms of current training methods and learning “on the job” from an equally improved quality of opposition - at least as it was around 1964? Finally, with all that, no matter how much experience Jess accrues and applies to his best advantage, it might be understood that, as it goes from one individual to another, there are still inherent ceilings to mental and physical potentials and achievements. Just considering two non techno attributes that were cornerstones of prime Ali’s success - speed and reflex - 50 years of experience will not bring Big Jess any closer to Muhammad in those significant regards.