John L Sullivan was the best heavyweight in the world from 1880 till about 1890 or so, and most of this time second place wasn't even close.
Take it up with Adam Pollack. It's his argument. His contention is that the distance between Sullivan and his nearest contenders was greater than at any other time in the division's history.
this 'might' be true in as far as the men he fought, but did he fight the actual best, or the financially backed/owned fighters presented him, rather than a few that might not have been in the possession of the money men that mattered, therefore "not ours, no play". Boxing could be rewritten, as I have said many times.
I do not know the answer but, unless I am mistaken hardly any of the responses are responding to the actual question. If I am wrong I am quite positive you will all beat to within an inch of my life. I have always thought of peak as the very best of a boxer's prime years. Ray Robinson and his 129-1-2 record has been mentioned often but those numbers start at the beginning of his career and he was hardly in his prime, let alone his peak, in the early 1940s. The same goes for many of the fighters mentioned. Prime and peak are both areas of opinion and, as previously stated, I don't know the answer but I will throw out this modern-ish example. From May 1994 to September 2002 Roy Jones had 23 bouts which included 20 or 21 title fights. Those fights included 152 complete rounds which would equal 456 rounds of judges scorecards. Jones was the winner of 424 of those rounds and lost just 32. This does not count the 12 rounds where he KOed his opponent or the round he was DQed after putting Montell Griffin on the canvas. Basically, Jones won better than 13 of every 14 rounds over an eight year period. That is quite a peak.
this is good work and yes, a good break down of a fighter's career and on point to the Thread. however, I was looking at the longevity part too, which 8 years is long, sure it is, but that is a relatively low number of fights compared to say a 10, 12, 15-year period where a fighter might have reached dozens or hundreds of fights with relative & contextually few losses... so yes, dissecting such records like that further as your good work has done with RJJ, it would still probably reveal some great, great and amazing records. But yes, you are on it. and I don't know the answers either, but some of our great informed posters might know of a few, it is a hard question on the surface, but yes, like you have pointed out.