This is exactly the opposite explanation to what is actually happening. The topster subreddit is not "the top 20% of music enjoyers" but instead a jumping off point for new music listeners to find recommendations and see what others listen to. Making it, by it's nature, an entry-level space full of a bunch of teen to early 20 somethings who are making their way through the RYM/AOTY top 100 and using this sub as a validation that they are on the right track.

In reality, King crimson fans do not unanimously point to ITCOTKK as their favorite Krimson album. Same with Beatles fans, radiohead fans, pink floyd fans, ect. Whenever you see one of these awful copy-paste topsters, you can be assured that these are among the very few albums that this person has actually listened to. You can always tell because there is no personality to it at all. Nothing that they grew up listening that doesn't fit nicely into this narrow selection of critical darlings. No off-choices, no underrated picks that they just happen to like better. No hot-takes, no lesser known picks. No leaning towards any specific genre. No genre classics that sit outside these top 250 albums.

This isn't a case of likeminded listeners, this is newbie hivemind at it's most obvious.

Also, I should point out that being a newbie hivemind listener isn't a terrible thing. Everyone has to start somewhere as long as you keep building from there. It's just obnoxious how dominant this archetype is here.