I have a lot of respect for Sullivan. Adam's book really highlighted how good he was in his day. (Colour line noted though) Surely though, in over 100 years the sweet science must have progressed a ton. I dunno, this is such an abstract fight in many ways. Sullivan may have been an outlier for his day. Or maybe if film existed, we'd all be very disappointed. It's anyone's guess. I think it's safe to say that Wilder in Sullivan's era, at least from a purely physical point of view, would have looked like someone from another planet.
I get the idea that Corbett was a guy who relied heavily on his reflexes, like Jimmy Slatterey or Roy Jones. Other fighters likely didn't have the reflexes to replicate his style. I am not saying that he didn't have some good tricks, but I think that Bob Fitzsimmons would have been a better model to copy for a novice of the day.
So were ballpoint pens. (LOL) People were easily impressed back then. There wasn't a lot going on. (A writing instrument you don't have to dip in an ink bottle? WOW.)
The film can be interpreted a number of different ways. Even if Corbett was as bad as you say, you would be making a massive assumption. For example if Artur Biterbiev, had to fight with the same style as Corbett, or in the bareknuckle stance, against a state level heavyweight, would that be enough to close the gap?
What I see is a novice by todays standard who was fighting, even less educated fighters a product of the times it was the caveman era of boxing and he was still not looking impressive against them. good for his time yes, good in general, naw.
The problem is that you don't have a lot of data here. What if all that you had from the 00s, was a couple of Roy Jones fights, with the timing all over the place? Would you assume that Jones was the pinnacle of technique for that era? What if the top fighter of the teens was Carl Froch, and the timing was off? Boxing manuals of that era, are not very different from those today. Even if these guys were as bad as you say, raw talent wins through at some point! When Joe Louis was signing autographs, anybody was welcome to throw a punch at him, and he would just block it. That is what you ae up against at world level.
So many changes from the sport in 120 plus years. I mean yeah perhaps todays heavyweights can beat Corbett in a 12 rounder. But put them in thongs and have them wear horse hair gloves and make the fight 25 plus rounds, oh yeah and the rings SUPER Large, and you may see a different kinda of fight.
I have film, I see Corbett he looks garbage, I have film of other ATGs with brain damage who impress me more.
