Originally Posted by
LeonKeyh
It does have to do with the stat squish, at least partially.
Whenever the stat squish happened, doing unsynced content would be more difficult. I don't remember the exact numbers, but 1-50 remained unchanged and 51-80 was reduced with 81-90 matching the Shadowbringers stat growth. This means that level 90 characters are "weaker" than they were at level 80 (and also, right now, don't have the highest ilvl for expansion cap). For DF content, they made up for that change by giving buffs whenever doing unsynced content; However, those buffs didn't carry over to the overworld (obviously).
I doubt that they changed how powerful the A ranks were to other characters at that level; It's just that level 90 players are "closer" to it stat-wise than level 80 players were.
Edit: I agree though, this is a good thing. They should be available for groups; Find your DC's hunt train community if you want to take them out!