I was curious about goblins specifically, so I spent half an hour or so skimming through their write ups. It turns out that they are actually one of the more consistently presented races, and yet...
- They have drifted from their original lawful evil alignment (1e/2e) to neutral evil (3e), to just evil (4e), through to 5e's prevarication.
- In OD&D they hated dwarves so much that they would attack on sight. This antipathy gradually faded through editions.
- The 1st Edition Monster Manual implies that they may be related to kobolds. This is a relationship that continues to be mentioned throughout 1st and 2nd Edition, until kobolds became something different in 3e.
- BX and BECMI give goblins eyes that glow red in the dark. They don't seem to have these glowing eyes in any other version.
- Until 3rd Edition, goblin aversion to sunlight is constantly emphasised. Yet from 3rd Edition onward, this seems to have been entirely dropped.
- 4th Edition implies that goblins may have been the magical creations of the hobgoblins when the hobgoblins ran an ancient empire.
The revelation in
Monsters of the Multiverse that goblins were originally fey makes it clear that goblins themselves are unaware of this distant history. In that sense, this is "additive" lore, in that it doesn't detract from what was previously understood, it just adds another layer. Mechanically, goblins now gain Fey Ancestry giving them resistance to charm. This is a change, sure, but not something that is likely to have a massive impact on how PCs experience goblins in practice.
Bottom line: I'm not convinced that "but this changes everything we know about goblins" is a reason for disliking the recent changes that stands up to close scrutiny. Would the new goblins be more acceptable if they were glowing red-eyed, sunlight averse, compulsive dwarf killers, who were magically created by hobgoblins before they became fey?