Absolutely no reason at all for them been lvl 90 content. I don't really follow lore, but most of them seem relevant at 85-89. Green stone village one would have been perfect for a level 85-86 as it takes place in Jade forest. Made no sense at all for it to be lvl 90, would also ease the dungeon spam from 85-90 as you get 2 dungeons, per 2 levels and they just get stale, quickly. Add a level specific scenario in there every level and you got a nice balance.