What was paul morphys rating. What would his rating be now

#24
The remark was that the last 3 in post #4 would be below 2400.
The methodology however is questionable: it does not measure strength, it measures engine like play. Of course Morphy did not play like an engine: he played King's Gambit and Evans Gambit. The chessmetrics approach is more scientific: processed all historical games to retroactively establish ratings of old masters.

As far as the last three go, Steinitz and Lasker won what were considered to be world championship matches.  That would be a good substitute for the much weaker tournaments that allow a GM direct title, so they would make GM even if the post #4 ratings were accurate (which I have doubts about). Morphy's career was too short to have what all would have considered a world championship match but the way he dominated the opposition indicate that he would also have likely earned at least a direct title.

That said, playing a clear win even if it takes longer than a tactically brilliant one may not do as well on CAPS but it is effective in the real world  When you are playing weaker opposition you reach more positions you can simplify and win without going into the CAPS-improving complexities that are available.

#26
Morphy defeated Anderssen 8-3 in a match.
https://www.chessgames.com/perl/chess.pl?tid=79263 

I'm not sure about that. Morphy was familiar with games of his contemporaries. Also, Morphy wrote 52 chess columns for the New York Ledger in 1859 and 1860 in which he annotated 35 La Bourdonnais-McDonnell games as well as a few of his own and others.

It's true that Morphy didn't work at the game the way modern titled players do, but the idea that he never studied is a rather an hyperbole.

So he also is at least a direct title GM.

#29
Morphy also defeated Paulsen 6-2 in a finals match.
https://www.chessgames.com/perl/chess.pl?tid=79271 

@blueemu I've always had issue with that CAPS chart. A huge percentage of games in Morphy's database are from casual games, simuls, and even blind simuls. I'm sure a lot of those other players will have much lower scores if you included a ton of those types of games.

Direct GM titles are awarded (upon getting a 2300+ rating) for reaching the final 16 of the World Cup or for winning the Continental Championship (or for other things, but those two are enough).  Morphy was the top American (beating the only other contender in the Americas).  Considering the matches he played it is reasonable to see him as one of the top 16 in a World Cup equivalent.

I think the more interesting question is how Morphy would do in Chess960 against modern players. The main edges that every strong current player has over Morphy is an overwhelming advantage in preparation, knowledge of previous games played, and knowledge of opening theory. If the players just have to rely on their positional and tactical skills, the playing field would be much more level.

#33
"The main edges that every strong current player has over Morphy is an overwhelming advantage in preparation, knowledge of previous games played, and knowledge of opening theory."
Opening theory does not matter. An engine destroys any grandmaster from any imposed bad opening imposed on it.
Look at this famous game between 2 humans. White is better prepared, but black finds all the correct moves over the board. In the end black errs in a table base drawn position.
https://www.chessgames.com/perl/chessgame?gid=1993385 
Other famous example
White was better prepared and plays his first 19 moves in 5 minutes. Black had to find all his moves himself and used 90 minutes for this. Guess who won...
https://www.chessgames.com/perl/chessgame?gid=1139797 

Yes, openings and prep don't matter, which is why all the top players spend their days studying theory and preparing against their opponents. Honestly, presenting a couple of games is the worst kind of argumentation. It's called the anecdotal fallacy and proves nothing about the more general claim. I could show you a picture of a penguin and say it's proof that birds can't fly even though there are only 57 total species of bird that are flightless. Presumptively, if top players spend their days doing it, it can't be a waste of time.

Kasparov did some interesting analysis of some of Morphy's games, in the first volume of his book, "My Great Predecessors".

In it, he repeatedly used the word "grandmaster", when evaluating Morphy's moves and ideas. Note how he didn't use the words "International Master" or "FIDE Master" as levels of comparison, which he could've just as easily done.

From that we can conclude that, in Kasparov's eyes, Morphy demonstrated the understanding of a modern grandmaster.

(Fischer suggested Super GM, which is an even grander declaration ...)

But I'd say that a time-travelling Morphy would certainly be strong enough to reach 2500+ FIDE in today's era. *

* (If in good health, with sufficient motivation, and if given enough time to familiarize himself with modern theory ...)

#37
Openings and preparation are minor factors.
The better player always defeats the better theoretician.
Here is another famous example
Black had secretly studied and prepared his gambit for years.
White sees it for the first time and refutes it over the board.
https://www.chessgames.com/perl/chessgame?gid=1095025 

     It's impossible to get a reliable rating for 19th and early 20th century players using computer accuracy comparisons. The opening theory of the time encompassed many moves that have over time, in hundreds of master games, eventually been proved to be less accurate than the present-day choices. To say that a player is "only" 2450 strength rather than 2700+ because they were unable to work out over the board refinements that took generations of GM-strength players decades to perfect is absurd.

     Another factor is the weakness of the competition. Morphy knew he could overwhelm most of his opponents in a wild, complicated tactical situation so he didn't hesitate to make what the computers consider unsound sacrifices. Notice how his matches start out fairly even for the first 4 or 5 games, but after Morphy has taken the measure of the opponent's abilities he rolls them up decisively. Lasker frequently played moves that he knew were inferior just to create difficult unbalanced positions where he felt his superior abilities would prevail.

TBH he would probably be around 2100

He would kick any 2100s butt 100 times in a row.

No

Morphy would wreck any modern 2100. It'd be a massacre.