This long-asked, yet virtually impossible-to-answer question might finally have a starting point. Of course, without the invention of a time-travel device, the true answer to this question will forever remain a mystery, but with Chess.com's CAPS, we may at least have a yardstick capable of comparing all players to the same standard.
https://www.chess.com/article/view/who-was-the-best-world-chess-champion-in-history