Jeffries won because his body attack broke Fitzsimmons down.
Whatever his age and weight, Fitzsimmons was still a terifying fighter.
I think that the training footage has to be taken into acount.
Jeffries won because Fitz smashed his hands on his head , he was also fighting with a dislocated thumb.
Hype Igoe who was ringside stated it was the worst beating he ever saw one man inflict on another ,worse than the beating Dempsey gave Willard.
Training footage means nothing imo .
Footage of Johnson training shows a very mobile, never stationary heavyweight busy with both hands constantly going.
In fact Johnson fought nothing like that .
The film we have of Jeffries fighting shows him laying back and countering against Sharkey,and plodding forward against Ruhlin, and Johnson.
Throw out the Johnson debacle ,that leaves us with him in his prime against Ruhlin ,who appears quicker afoot ,and better defensively.