They should really move unobtainables from removed quests somewhere else.

[Iscah]

Off the top of my head the "Lighter than Air" title you used to get from unlocking flying in Tailfeather. That quest was removed when they shifted the unlock to completion of ARR.

Not many probably noticed but for example Feast went away and it had achievements with titles/accessories that were tied to playing as a premade and winning matches but those were removed instead of changed to include "Crystal Conflict" like the rest of the achievements

Yes, things have been made unavailable – but where are they currently that they can be "moved somewhere else" as has been requested by the OP?

Are they still listed in the achievements menu? I don't recall seeing anything unobtainable in there.