I did not do all the hat quests, but my observation is that in the very difficult areas, mobs were adjusted to be less dangerous during the hat quest. I think that after the hat quest was over, no one ever went back and readjusted the mobs. For example in the Savrenoc Stronghold, the Elves were hardened and blue before the hat quest and the difficulty was a 4 skull area. After the hat quest, the Elves are regular elves, but the difficulty still shows 4 skulls when really it is a 3 skull area since the quest. It might be prudent to investigate if there are any more loose ends to close now that the hat quests are done.