Well, this ranking is something.
My first impressions:
The ranking is of course highly biased towards North American athletes. Which shouldn't surprise as it was ESPN that has created it.
There are some good and some horrendous takes, and some that are highly debatable.
Michael Phelps being #1 is somewhat understandable considering that he has won the most Olympic medals. But it's a great advantage being responsible only for yourself and having the chance to win multiple medals within the same sport and the same Olympics. That's an advantage most athletes simply don't have.
Serena Williams at #2 is highly debatable. While she is certainly the most dominant female tennis player of all time, she might be the person in the top 20 or so with the easiest path to excellence, because tennis itself is an expensive sport with a relatively low number of participants, but female tennis in general isn't a sport of the masses. Probably 1/2 of the female world population will never have the chance to play tennis even as a simple hobby, let alone competitively. There are like 40-50 countries where women have the resources to play tennis on a high level, and maybe 10 where they have the opportunities similar to those in the US, which makes for a small field of competitors.
For this reason as well, Messi at #3 is rather laughable. He dominated the most played, most competitive sport for a decade and is considered by many to be the greatest player of all time.
To stay on topic: Henry definitely shouldn't be ahead of Zidane, Modric and Iniesta.
Hamilton ahead of Schumacher is insofar correct as Schumacher's success goes back to the 90s. However, if they evaluated Schumacher as a whole, I don't think there should be any F1 driver beating him.
McDavid at #98 is hilarious, though. There hasn't been a player since Lemieux and Gretzky who has been so superior to his peers and put up numbers like he does. Crosby ahead of McDavid is plausible if cups are taken into consideration. But there shouldn't be a gap of 66 spots.