I I think you have to look beyond the absolutely dominant champion from the time to see how much the sport has evolved, if any. What did the top 50 Heavyweights of the day look like compared to today, for example? How about the top 10 from around Louis' peak, vs. the top 10 from today (#1 vs #1, #2 vs. #2 etc..). So, from The Ring's annual 1938 top 10, vs. today's... Champion: Oleksandr Usyk (6'3" 221 lbs.) vs. Joe Louis (6'1" 198 lbs.) 1. Tyson Fury (6'9" 281) vs. Lou Nova (6'2" 198) 2. Joseph Parker (6'3" 267) vs. Max Baer (6'2" 210) 3. Agit Kabayel (6'3" 241) vs. Bob Pastor (5'11" 190) 4. Daniel Dubois (6'5" 248) vs. Tony Galento (5'9" 227) 5. Anthony Joshua (6'6" 252) vs. Maxie Rosenbloom (5'10" 180) 6. Filip Hrgovic (6'6" 247) vs. Len Harvey (6' 181) 7. Fabio Wardley (6'5" 241) vs. Clarence (Red) Burman (5'11" 186) 8. Zhilei Zhang (6'5" 287) vs. Roscoe Toles (6'2" 196) 9. Martin Bakole (6'5" 299) vs. Gus Dorazio (5'11" 184) 10. Moses Itauma (6'2" 254) vs. Tommy Farr (6'1" 208) How many Ws do you see the 1938 crowd getting here? There would need to be a deeper dive than this of course to really see how much evolution has taken place, but this is a start. When talking about the evolution of the sport, I'm talking strictly Heavyweights, where the bigger, stronger, faster part of it maybe comes into play.
Honestly, I'm not familiar with most of the fighters from the above top 10 list from '38, so I couldn't begin to break down how these fights would go. The size difference jumps out in most of these. Tony G. gets sparked BTW, but Dubois was in quite a bit of trouble vs. Lerena, so maybe that's fun while it lasts. Anthony Joshua vs. Maxie Rosenbloom is just a weird matchup. Not sure how on Earth a guy of Maxie's size with apparently zero power gets that done.