Aha, I love a good hypothetical..
Todd has a good point, those albums ARE already regrded by millions to be THE best albums ever made, speaking as a lifelong prog fan who has a collection of over 1000 prog albums and spent years posting on prog boards, I can assure you this is fact eraser...
But this is what it is, hypothetical, they didn't make those albums, those albums are not in the style of The Beatles in any way, 'In The Court' was probably the first prog album ever made and is fantastic, but its not mainstream music.....which the Beatles WERE, appealing to kids, parents, even grandparents......I love 'Court' when it came out, it was a whole new genre, blending other genre's, but not for one minute, would my parents have listened to it (they were fans of the Beatles), they would also have not listened to DSOTM, as it was way too weird for their tastes, of course I loved it, so in essence, no, I dont agree with your hypothesis, I dont think the world would have declared them the best albums ever made...they just weren't accessible enough to the public at large, The Beatles wrote songs that people could sing and whistle, great melodies that will live forever, you cant walk down the street and whistle Schizoid Man or The Great Gig In The Sky (maybe Money you could )
Another point is, I dont think the Beatles made 'the worlds best album' what they did though was consistently make very very good albums, each one (with the odd exception) being better than its predecessor, both Floyd and Crimson didn't manage that, they just made these stand-out albums, that are regarded as classics, Crimson couldn't repeat that achievement and went on to make inferior albums (with the possible exception of Red, although it wasn't ground breaking)
Floyd had a very mixed bag of good and not so good, they made several albums after DSOTM but none were as good it has to be said, although WYWH is a high point.
The Beatles were leaders of a social revolution in the 60's (I was there) and theyre importance is immense in that role, as Ive said, when over 20,000 cover versions of your songs are made (by some of the worlds leading artists) I dont see how you can be overrated, you are what the public make you, and The Beatles were massive.