... Collectively, Morphy's score against Adolf Andersson ... was twelve wins, three losses and two draws. That is unheard of. These aren't casual games, either, they were matches.
I only know of one Morphy-Anderssen match.
"... The score stood Morphy seven, Anderssen two, and two drawn. ... The next day, while photographers were arranging for the group picture ..., Morphy and Anderssen played six offhand games in three hours, of which Morphy won five. ..." - David Lawson (1976)
... Adolf Andersson ... was later contender for world champion against Steinitz ... Andersson was considered the strongest European player in the late 1850s and Morphy beat him easily. If he did that, then my reason suspects me to believe that he also would have beaten Steinitz easily. Either way, it puts Morphy at world-champion contender level for that time.
I have seen no record of an 1866 statement that the Anderssen-Steinitz match was for the world championship. In the 1870s, on the basis of the 1866 match and other competition results, Steinitz did argue that he had a claim to the title, but it was in 1886 that he played a match (against Zukertort) that was described at the time as a match for the world champion title. Long before all that, Morphy had indicated his desire to no longer be involved in such competition.
I think the argument against Morphy is that his opponents were terrible, but if you can give me the name of one professional opponent Morphy didn't clobber OTB, chances are I haven't heard of him. Morphy was so good he made people look bad.
"... Morphy became to millions ... the greatest chess master of all time. But if we examine Morphy's record and games critically, we cannot justify such extravaganza. And we are compelled to speak of it as the Morphy myth. ... [Of the 55 tournament and match games, few] can by any stretch be called brilliant. ... He could combine as well as anybody, but he also knew under what circumstances combinations were possible - and in that respect he was twenty years ahead of his time. ... [Morphy's] real abilities were hardly able to be tested. ... We do not see sustained masterpieces; rather flashes of genius. The titanic struggles of the kind we see today [Morphy] could not produce because he lacked the opposition. ... Anderssen could attack brilliantly but had an inadequate understanding of its positional basis. Morphy knew not only how to attack but also when - and that is why he won. ... Even if the myth has been destroyed, Morphy remains one of the giants of chess history. ..." - GM Reuben Fine
I do not know if KholmovDM counts things like the Fine quote as "argument against Morphy", but extended discussions of Morphy have been written in books by GM Franco, GM Beim, GM Ward, GM Marin, GM Bo Hansen, GM McDonald, Garry Kasparov (with Dmitry Plisetsky), and GM Gormally. Anyone see any of them express disagreement with Fine's main conclusions about Morphy's standing in chess history? Has anyone seen any authority express doubt about the quality of Morphy's opponents having been well below what one would face today? It is perhaps worthwhile to keep in mind that, in 1858, the chess world was so amazingly primitive that players still thought tournaments were a pretty neat idea.
You can argue he'd get clobbered today, but that's like saying Archimedes would be dumbfounded by a 737 flying overhead today. ...
It seems to me that it depends what specific question one is discussing. If one is discussing the claim that Morphy would defeat anyone today, it seems to me to be appropriate to consider the degree to which we have evidence to confirm that idea.
https://www.chess.com/article/view/who-was-the-best-world-chess-champion-in-history
... Those players albeit weren't very strong, so therefore Morphy was terrible because anyone can give blindfold simuls to more than eight people at a time, spot material, and win perfectly (cough...)
Can you identify a specific Morphy event that fits that description?
... Staunton purposely avoided playing against Morphy for fear of humiliation. ...
It is perhaps of interest to look at an 1858 comment of Boden:
"... Staunton ... that he is now the champion, even of London, alone, over the board, we unhesitatingly deny - and this fact is notorious enough in this country, while on the Continent the idea of his being considered the champion of Europe would be ridiculed as the height of absurdity. ..."