Aside from mechanically difficult bosses, the dungeons could do with some mechanics outside of the boss fights.

Let's use Amdapor Keep Hard Modes potential trash room between the first and second boss. The room is a linear pathway, BUT, the walls are all Demon Walls. There's a Lamb of Dalamud Priest standing at the end of the hallway who awakens the walls as well as summons a barrier to keep players from running through when they make it to the end.

That's not all, as there are mobs on the way to said Priest, with each group containing one unique mob that makes speed running the worst idea possible (it's also stationary). Should the party try to do the usual "grab them and then move on" strategy, the stationary mob will use 'Draw-In' on the entire party, which will also throw on a stackable Heavy debuff (three stacks will cement the party in place until the group of mobs are destroyed).

To make matters worse, players can not focus on killing the stationary mob first, as the group around it will instantly cast a Raise type spell on it (so if a party decides to kill it first and then pull the rest of the mobs to the next group, the other trash will revive the mob, which will then pull the entire party back to where it died). While you're fighting these mobs, the Demon Walls are constantly attacking the party with Murder Hole, while also slowly covering the floor with that purple goop we're all familiar with. And to be mean, the stationary can use Repel, which it will instantly follow up with Draw-In and then a Gravity spell.