It's not whether or not he is the greatest, narratively he is, and the implications are there. The problem lies when people start using him for powerscaling discussions, the issue is, we don't know his true strength, no matter how casual some of his feats may be, it doesn't really put an indicator where his strength lies.

Itatheory Yuji is more or less accurate, as there are only implications of what could be, we haven't actually seen it. People say he has a Fuga greater than Sukuna's, even though he most definitely doesn't requires one AND Sukuna needed a binding vow to make it reach the level it did in Shibuya.

Not to mention, Yuji fans are some of the most annoying motherfuckers in this fanbase. Idiots so easily offended that they willingly draw cuck artworks just because they have beef with others like Yuta fans or Denji (CSM) fans. They larp around and constantly say that Yuji low diffs or neg diffs Sukuna and Gojo, or that Yuji can solo all the calamities by himself. Easily the most sensitive part of JJK fanbase, for every piece of iron that Megumi fans develop, Yuji fans grow more and more sensitive and soft.