There has always been great fighters in the heavyweight division, the main problem is when they introduced the cruiserweight division it completely ruined the heavyweight division, and most organisation put in a minimum weight restriction to fight for belts, when you look closer a lot of the all-time greats like Joe Louis, Rocky Marciano, Joe Frazier and many others would weigh either dead on or just too much for cruiserweights these days but not enough for heavyweight.
It gets banded about "he got knocked down by a cruiserweight" by idiots about various heavyweights, and because fighters between cruiserweights and heavyweight aren't allowed to fight at their natural weight, most ,of those smaller heavyweights are not as quick or lack effective stamina to trouble the giants these days.
Tyson and Ali, Foreman and Holmes were all big heavyweights back in the day now they're quite small for heavyweight bar Foreman, who is still fairly big but not massive like peeps thought of him in the old days.
There has always been giant heavyweights in the past and good ones too but the likes of Marciano who is criminally underated, with his stamina speed toughness and brutalising could've chopped down the likes of Lewis, both Klitschko's and Fury too, people don't realise Marciano was incredibly hard to hit cleanly but he was ... Tyson Fury is world class and at his current level would give anyone in history problems win, lose or draw.
Having said that though the likes of Frazier and Marciano or Dempsey are the brawlers are the types who used to brutalise the big giants in those days, Tyson Fury's footwork, hand-speed dark art/dirty tricks and ring IQ with his towering size and heart would defo cause problems for most in boxing history.
Not saying he would be one of the absolute greats but styles make fights.