Ali was only considered the greatest because of everything he did outside the ring. Fury is doing the same by raising awareness on mental health. He's pretty much locked for sports personality of the year.
Put them both in a ring during their primes and it wouldn't be fair. Fury is 6 inches taller and fights 4 stone heavier. Its likely that Ali today would be a cruiserweight, not a heavyweight.
Fury He spent his career being underestimated only to toy with Klitschko who is one of the greats. Its not even like he struggled. He then fell into depression with drugs only to announce his return, lose 10 stone, be denied victory for the greatest comeback fight in decades (american judges for you) then returns and knocks out an actual knockout artist. It was a complete one sided domination and a big 'fuck you' to american corruption within the sport. The guy has been an entertainer in the most humble way.
If he deals with AJ as swiftly as he has everyone else then it really cant be denied that he's the greatest heavyweight theres been. Ali lost 5 of his fights and struggled against taller opponents. Fury would simply have been too much for him.
As for old school fighters, like all greats they are only truly recognised as GOAT's long after their time. There's more science and skill in boxing today rather than old school rocky like fights. 20 years from now if Fury keeps this up he will be hailed as the GOAT.
Regardless Fury's is a true underdog story and i'll expect their to be movies about him in the future