Yeah I might also be confused as well but I thought the discussion was around putting all Aberrations in one section, all Monstrosities in a section, etc. I have no issue with putting all variants of, let's say all variations of "Dragon, Age Color" or "Giant, Element" together. It's still organized alphabetically under D / G because the monster is "Dragon, Ancient Black" or "Giant, Fire", and then there are a bunch of variations on that monster at differing CR values.
Demons/Devils don't exactly fit the same argument, I feel like that organization only really works because "Demon" and "Devil" are right next to each other in the alphabet so you don't actually have to remember which is which (and Yugoloths being separate only works because no one has ever looked for Yugoloths).