If you dont think sports science has given a advantage to athletes in the last 20 years, then you should really do some research.
Uh what kind of research?
Freaks of nature like Lindros, Pronger, Lidstrom would still completely dominate a modern NHL game.
There is no supplement available today legally that can increase performance that much and I hate to break this to you but people knew by the 90s that getting sleep and not smoking were important.
There isn't that much that has changed since the 90s really, the fact that creatine really was the last huge supplement craze and there has been no supplement product since then to really supercede it kinda shows that too.
There's nothing in any supplement store that you can buy today that wasn't available 20 years ago that would radically alter ones stamina, muscle mass, fast twitch muscle fiber, or muscle recovery to any massive degree.
If such a product existed and was legal, everyone and their grandma would be taking it.
These guys do "new age" stuff like the ice bath, but that's nothing special either, athletes have been putting ice bags on their knees for 20-30 years at least as a common thing. The Chicago Bulls were doing that all the time in the 90s.