We would have to conclude that Sullivan was pretty darn durable. His only stoppage loss in over a hundred fights, was in his last fight against Corbett.
The hardest puncher of Sullivan's era, possibly including Sullivan himself, was Frank Herald, who Sullivan beat in a shoot out. Jimmy Elliot was also a very dangerous puncher.
I really like Fitz but, this was the most brutal era in boxing history, and from everything I've read John L. Sullivan was it's most brutal fighter. His strength and savage power carries the day in a fight that leaves him ruined.
It seems that Sullivan had times when he could not finish even relatively men or the fights went forever. But I believe this was due to a combination of fights after his prime, + that the opponents often frequently took a knee in order to avoid being KOed, correct? If so, then maybe most anyone would have great trouble braining someone who could continually take that pause & reset. It is similar to of constant clinching is allowed. Tyson was not really unimpressive against Green & Bonehugger, they just world class, strong, huge fighters who were willing to grab often in order to spoil.
Sullivan's Queensbury fights were usually scheduled for 4-6 rounds, so he didn't have that long to put his opponents away. Also the Police frequently stopped fights, if one man was on the verge of being knocked out. The contract usually sated, that if the Police stopped the fight, the fight went to the man who had the other man in trouble. In is bare knuckle fights, and opponent had thirty seconds to come up to scratch, after a knockdown or a throw. This meant that if you had a man in trouble, he would often take a knee to get thirty seconds respite. If an opponent was determined to spoil, it was very hard to put them away.
Post 1884, the quality of Sullivan's opponents increased, though none of them were world class. 4-6 rounds is enough time for a puncher to put his man away, yet I see way too many distance fights. Put the same opponents in vs Fitz, and their looking up at the lights. Just how hard Sullivan hit is a guess. If he hit as hard as some think, then perhaps accuracy was the issue.
Hearld? The guy was tiny, and chiny. He did not beat anyone I recognize on his resume. The Sullivan vs Heard fight looks like a foul fest that went two round whiteout anyone being hurt. Hardly proof of anything. [url]https://boxrec.com/en/proboxer/32592[/url] [url]John L Sullivan[/url] beat [url]Frank Herald[/url] by TD in round 2 "); margin: 0px 0px 1rem; padding: 0px 0px 0px 3.5ex; caret-color: rgb(33, 37, 41); color: rgb(33, 37, 41); font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji";"> Date: 1886-09-18 Location: Coliseum Rink, Pittsburgh, Pennsylvania, USA Referee: [url]Johnny Newell[/url] Herald was known as "the Nicetown Pet." This bout took place at the Coliseum in Allegheny City, a suburb of Pittsburgh, Pennsylvania. It was the first match in over a year for Sullivan, the world heavyweight champion. Three thousand people attended. Because several prior attempts at a Sullivan-Herald fight had failed to come through, Herald's backers insinuated that Sullivan was scared of their man. However, Sullivan was much larger than his opponent, outweighing him by as much as forty pounds. Sullivan used his size advantage to drive his opponent to the ropes through much of the first round. The second became a wrestling, holding, and fouling match until police intervened. Sullivan was afterwards declared the winner.
I don't think there is any doubt regarding Sullivan's power or his speed of hand and foot .. there are legitimate questions on his style, defense and quality of opposition , specifically for M of Q caliber ... from what I can gather from what I have read, Sullivan was kind of a Deontay Wilder meaning specifically he had one style and it was a devastating style .. I've read time and again that he never sparred, never threw a jab, just came in like Sullivan to destroy and we all know that can have it's limitations against a highly skilled fighter .. I have trouble seeing a one dimensional fighter with virtually no defense standing up to too many of Fitz's bombs .. It's not just that Fitz was one of the all time great P4P punchers but he was a highly skilled, highly experienced fighter , far more than Sullivan ..