Don't think you grasp the theory of evolution .... I'm starting to think you’re new to the human race
Man / Woman get better every generation, not guesswork but fact, just look at world records in every sporting activity and they are constantly being improved. That's not hard to understand with medicine, diet, conditioning and training methods all invariably improving it's to be expected.
Football is exactly the same, players are faster, stronger, fitter than they were a decade ago and on a completely different planet to their smoking, drinking pie and mash eating counterparts of the '70's.
To imagine the richest sport on the planet has not seen the highest level of player development is naive, as for managers? The argument has little merit, given eleven stronger, fitter, faster players you or I could manage a team to beat Wenger or SAF's team of 20 years ago ....
You're saying that physical improvement is a factor of management, not really, the best teams, the same teams, have dominated Europe for decades with dozens of different managers. Having the best players is what matters, the manager is just the final piece ... if not Forest Green would appoint Wenger/SAF and be EPL champions in three years ...