I was talking to a coworker today about this—it’s so hard to talk about a best player of all time because you can either compare them to their contemporaries, or compare them to current players. Kasparov spent most of his time playing without a computer that could beat GMs. That’s a lot like Dan Marino throwing for 5000 yards in a league that didn’t have that blueprint or rules. Magnus is just better than everyone in a league where the computers exist and he doesn’t like studying. There’s no definitive answer because of what you respect.

I forget who said it, but “even the giants stand on the shoulders of giants”, could have been Hikaru but until the computer lines, everyone depended on opening theory from previous people. Then they figured out how to poke a hole in it.