The Fitz that fought Jeffries the second time The version of Jeffries Johnson fought. The Corbett Jeffries fought the first time. If these three guys, all in the same condition as when these fights took place, all squared off against one another, who comes out on top?
I think Corbett. Fitzs from Jeffries 2 was still brilliant, but he decline became very clear soon after, I don't think Corbett would have been much worse in Jeffries 1, than when he fought Fitz, and Jeffries against Johnson was a mess.
How was he still "brilliant?" Seriously? He was 39 years old and hadn't fought in two years. What do you base this on? A couple wins he had TWO YEARS EARLIER when he was fighting regularly? How do you know Fitz's "decline" hadn't already begun when he stepped in the ring against Jeffries? Was Mike Tyson "Brilliant" against Lennox Lewis because two years earlier he stopped Golota and Savarese in a round or two? There seems to be one set of rules for fighters we can't see and another for fighters we can.
I would expect Fitzsimmons to prevail against both opponents. Yes a younger Jeffries caught up with him, but he needed to really force the fight in order to do so. The slower more reactive Jeffries of the Johnson fight, would just get diced up, with some sort of stoppage being forced eventually. I think that Fitzsimmons body of work after their actual fight, is somewhat more credible than Corbetts. If you are asking who is likely to do better than in the actual fight, and who is likely to do worse, then you would have to conclude that Fitzsimmons would be likely to do better.
His performance against Jeffries. Beating George Gardner over a year later, then Philidelphia Jack O'Brien almost another year after that. Also a good enough fighter can decline somewhat, yet still be brilliant.