Another thing that people commonly overlook in these "who was the greatest?" cross-time comparisons is that if someone from the past (Morphy, Lasker, Capa) were brought forward to our time, they would start absorbing the modern knowledge and techniques. Who can guess how strong they might be, after a few years of catching up?
It's pointless to speculate.
Yes, and, yes.
I have had similar discussions about greats in sports I have followed. There is almost never a point where there is consensus.
Michael Jordan, the best? How about Bill Russell.
Tiger Woods? Jack, Hogan, and a few others are in the conversation.
Willie Mays or Babe Ruth? Or Stan The Man? Or Marichal, or Koufax?
Comparing players from different eras is interesting, yes. However, they didn't compete against each other, so, any comparison is only our opinion.
A tournament between Morphy, Fischer, Capablanca, Kasparov, and Lasker at their peak would be amazing. Some of these players could really hang on in inferior positions, and some rarely got into inferior positions. Some had really great endgame technique, and some rushed the endgame. Some were pragmatic and some were principled. And then there is Carlson...