If we're including other goblinoids in the comparison, then we would also need to look at the changes to hobgoblins and bugbears between/within other editions. I haven't checked, but I strongly suspect that both of those changed more than vanilla goblins did. (I'm still a bit surprised by how consistent the goblin has remained compared to... well, most monsters really.)
I agree that the sudden change to fey seems like a more radical change than any one of the things on my list. It also comes a little out of left field to me. During a quick perusal, I didn't find any indications or hints in previous lore that goblins might be fey. I don't particularly
mind the new fey origin, but it feels sudden.
Looking at a full list of changes in
Monsters of the Multiverse, and following
@Leatherhead 's excellent
Let's Read thread. I also agree that the only (somewhat) comparable mid-edition changes to monsters would be from 3.0 to 3.5. Third edition relied heavily on crunchy numbers in monster stat blocks, so 3.0->3.5 had many more numbers change. In terms of lore though, early 5e to current 5e now seems to be comparable to 3.0->3.5—small changes all over the place, and a few creatures where, if you look closely, there are much more significant updates.