Jack Johnson and James J. Jeffries fought in 1910. Johnson win by last round knockout. If they had met five years earlier, I believe Jackson would still have won. Jeffries came out of retirement for the fight. Many considered him the true world champion because he retired as an undefeated champion. Jack Johnson was the colored heavyweight champion and lineal champion since 1908. ( I use the term “colored" because that is what the title is called. I am not racist against African Americans. I am one.) In 1905, Johnson was two years removed from being butchered in 3 rounds by Joe Choynski. He was embroiled in 7 fight rivalry with Joe Jeanette, posting a 4wins 2 losses—1 draw record. Though professionally this was a bad year in terms of winning percentage, the old cliché still rings true: Styles make fights.
Jack Johnson was a fast starter who would drag bouts out. He would dodge and counter with speed and power. His strategy was to tire out the opposition and make them take prolonged beatings. James Jeffries fought from a couch with an overextended left arm. His approach was to take punishment and tire out his opponent through attrition and toughness. Same goal. Get them tired and win. Different vehicle. One guy does it through punishment. One guy does it through depleting stamina.
Johnson wins because he is doing more punching. Jeffries style made him acquiesce to the fact that he is going to get hit. Johnson is accurate, fast, powerful, and has enough speed to dodge what little offense would be coming his way. Could Jeffries knock Johnson out? Absolutely, Johnson had been stopped already. But is unlikely, when using a style that waits on an opponent to attack against an opponent who's goal is to extend the bout after landing anything of significance. Based on their styles, the result would be a decision for Johnson due to activity l, or a late knockout for Johnson due to accumulation of damage ( same as in 1910). I believe in this because, Jeffries was training to get his regular style and form back that he employed as a fighter. That was the style he used and lost with.