a rating of 2638 means that morphy has a small but not insignificant chance of drawing even the likes of carlsen. i dont see morphy drawing carlsen or kasparov. too many gaps. think about it. he is outplayed in the opening because of modern theory, he is outplayed in the endgame because lets admit it, endgame theory in the 1850's was in its infancy. that leaves middlegame. can morphy tactics alone be enough to to otherwise balance out the discrepancies in opening and endgame reliably vs 2600 GM opposition,? i dont think so.
2700 today would run circles around him. his strength is prob closer to very strong aggressive IM's who make up slight positional inaccuracies with incredible tactical acumen. , BUt such glaring inadequacies in so many other aspects of his game would put a hard rating ceiling on him.
... The thread wasn't about his greatness, it was about his rating and playing strength.
One doesn't need a time machine to measure that. We can simply analyse his games.
Rating is frequently taken as referring to how one would do against modern players. We are not in a position to measure that for Morphy by any verifiable method. Some people want to write about what would happen if Morphy were brought back from the past and (with spectacular unfairness) forced to play with no preparation and forced to forget what he learned from each game. Others prefer to write about how a resurrected Morphy would do with preparation and learning allowed. You can tell that last group to stop if you want, but why should they obey you?