It's just a difference of eras and style of fighting in the 1900s/1890s compared to the 1980s. Imo Dempsey was the turning point in heavyweight title history that went from the 20-45 round fighting style to the solid 15 round style of fighting which showed much higher punch counts and is more recognizable as what we consider boxing today. Not that there's anything against what the prior champs did but if someone walked into a boxing gym today and fought like Johnson, Fitz, Jeffries, Corbett, or any of those guys they would probably be dismissed from anyone's mind as little more than a weirdo who can't box. However I will add that if the guys from today or the eras after Dempsey were fighting back in Johnson's day in the sun with little more than gauze, tape, and a thin layer of leather covering their fists for potentially 45 rounds they would be fighting the same way. Under Johnson rules it would be Johnson by knockout. If it's under Tubbs rules then it's potentially Tubbs by stoppage or UD if Johnson fights the exact same way he did at his peak.
This. Besides just the rule changes The equipment was like night and day. I think Johnson and even Ali would've hated the attached thumb on the glove. Some of Johnson’s defensive strategies would have to be modified, since in my opinion it isn’t as easy to parry punches with modern gloves. Also, I wonder how Johnson would perform in modern boxing boots that aren’t leather soled and the ring surfaces are a lot softer nowadays.
Tubbs was not only bigger and hit harder, he has a better jab and faster hands. The best way to beat Tubbs is with power and lots of thrown punches, that isn't Johnson.
A tricky question. Yes, I think he would have beaten Burns ( sooner ), and defeated the same opponents Johnson did. Whether he would have lost to Langford or Jeannette from 1909-1915, possibly Johnson title opposition is very poor; however those who did not get title shot in Langford, McVey, Jeannette, Smith, and McCarty were not.
I'm sure some will choose Jack Johnson to win simply because he was around a long, long time ago. Having existed in a foregone era seems to be a major component to winning H2H fantasy match-ups in the eyes of many a boxing scribe.
There are people among us who think that Tubbs at his absolute best loses to Tommy Burns and Jim Corbett at theirs. https://www.boxingforum24.com/threa...ing-would-beat-tony-tubbs-at-his-best.609859/
I would say that depends heavily on just how deep or shallow the talent pool was from ~1900-15. If it was much smaller than in the 80's Tubbs cleans house; if it was roughly comparable, he still has a decent chance of adjusting to the rule set and picking up the lineal title at some point (temporarily leaving aside considerations of the color line to consider the question of talent in isolation).