You think it's 100% that gymnast Latynina would be the equal of Biles?
Hmm, can't agree there.
With Phelps, there isn't judging to contend with in future evaluations. The distances will be the same, his times are what they are.
If his records fall, I'll think he could have competed in future eras... but that becomes just a guess. All I'll feel very comfortable saying is he was the best of his era.
Same thing with Bolt. You aren't going to convince me that if Scholz was transplanted from 1920, that even with the better training of today, he'd be the equal of Bolt. I definitely agree he'd be 'better' though.
Some of this has to do with equipment though.
Remember, they had the one Olympics where swimming records were falling because they said the suits were made faster. I believe they got rid of those suits too.
All sports have equipment differences over the years but in some cases, like say golf, the equipment ,may be better but the courses are also much longer.
The distance of 100 meters in the pool isn't changing but if they come out with some fast suit again, that changes the dynamic.
And of course the athletes of the 20s could be every bit as good. They would be training under current standards, doing current vaults, etc..