I'm obsessed with The Beatles. I think that their popularity, mass appeal, iconic status, marketability, cultural/musical influence, and historical impact are gargantuan, miraculous and undeniable. I also find their lore and mystique the most addicting of any band to find out everything about. Unlike these other musicians, you can legitimately sink down that rabbit hole and let these factors consume your life. If you treat your musical experience as an all-encompassing storybook narrative, The Beatles easily have the best one (it almost all feels too perfect to be non-fiction), in my opinion.
However, I strongly disagree with the notion that the above really has anything to do with how great an artist's music is, which is what I think of when I refer to "greatness," personally. In the case of The Beatles, the stars align so much (and the quality of their music is so close to matching it) that I come close to being willing to make that concession. However, there are other artists who I REALLY don't consider anything remotely close to being among the "greatest" who satisfy similar qualities, such as The Rolling Stones or Led Zeppelin, and there's no way in hell I can get behind that. It's the same reason I don't consider Star Wars to be one of the greatest films of all time, despite thoroughly knocking many of those (in my opinion, irrelevant) external aspects/outcomes out of the park. I think I'd be a hypocrite to treat it as a significant factor for The Beatles simply because I also incidentally happen to think nearly as highly of their music. At best, I might view it as a tie-breaker.
Usually, the above qualities have very little, if any correlation to how good an artist's music necessarily is, in my opinion, but I will say that I think The Beatles are an outlier that are about as close as I've ever seen to something with that type of universal draw having quality of output that I feel matches it (in contrast, I don't think things like Elvis and Michael Jackson come close to matching their reputation). Another reason that correlation especially does not resonate with me when it comes to The Beatles is because I think that the primary catalyst for their mass appeal and cultural impact is Paul McCartney over everyone else, whereas I'm significantly more impressed and appreciative of John Lennon's contributions over everyone else (for the record, I think they're both good). The things that make them huge are completely different from the things that make their music great, from my perspective. Songs like Yesterday, Let it Be, and Hey Jude are their most famous songs, but I personally find them pretty underwhelming and uninteresting compared to stuff like Tomorrow Never Knows, She Said, She Said, and Strawberry Fields, which is the type of output that I feel elevates them into greatness.
When it comes to my opinion of their actual (musical) greatness, they're in my top 5-15 but definitely aren't my #1. They have one album that I would consider an outright front-to-back masterpiece (or at least close enough-- Revolver), and 4-5 albums that I think are at least a few tracks short of that, with a handful of things about them that I personally consider outright flaws (usually but not always the token light-hearted McCartney or Ringo sing-a-long, such as Maxwell Silver's Hammer, Octopus' Garden, When I'm 64, Don't Pass Me By, or Honey Pie)-- then reasonably solid but not particularly incredible or needle-moving output after that. So when other musicians exist who I think have multiple front-to-back outright masterpieces without any flaws (or even just musicians with standalone albums that I think are better than Revolver-- although that's a flimsier argument), I simply cannot consider The Beatles better or greater. Let alone abide by this ridiculous concept of a unanimous, authoritative, "your opinion is invalid if you think otherwise" absolute greatest (like what was argued in the New Order thread).
When it comes to The Velvet Underground, they have two albums that I feel are far superior to Revolver, and another that's on par with it, so I would consider them a better/greater band on those grounds. When it comes to Brian Eno, I feel that he has both more masterpieces, a stronger peak, and far more prolific and consistent output than The Beatles, so that's a no brainer for me as well. Something like Joy Division is tougher for me-- I can maybe go along with The Beatles being the easy answer with that one, but with a bit of resistance. While I consider Closer to be as good if not better than The Beatles best album and Unknown Pleasures to be better than any of the others (and peak is what I appreciate above all else), that's like a near-tie in peak vs. a complete steam-rolling in every other area.
I would consider all of these bands significantly better/greater than The Stones/Zeppelin/New order (which are all completely out of the picture and barely make a dent for me), though, personally. Hell, you could tack on ten additional New Orders to the end of Joy Division and it wouldn't improve their case very much vs. The Beatles, IMO.