Some of the older dungeon and raid (primarily Alexander ones) bosses just need more HP and they should be relatively fine, but some of the trials and alliance raids need their min ilv caps reduced.

Any trial that is an expansion capstone fight (Thordan, Shinryu, Hades, Endsinger) gets heavily screwed over by increasing ilvs throughout the expansion, so all of those are going to need a ilv cap to prevent this from happening. A mega easy fight is not really a good way to end an expansion's story, especially when said boss is typically hyped up to be super strong and powerful. I've gotten Thordan a few times in trial roulette lately and I've had runs where we got him to 0.1% before he leaves.

As for alliance raids, Crystal Tower is just too easy and braindead due to item level. You can actually see this at play by looking at the World of Darkness raid. That raid's min ilv is much closer to the ilv cap for ARR, and it shows as the mechanics actually matter to an extent and are dangerous enough to kill you. I personally think that the World of Darkness would be a good standard difficulty for ARR alliance raids. Thus, I think a max ilv cap should be introduced to LotA and Syrcus Tower to try and emulate that same difficulty level. This would also technically re-introduce mechanics to those two raids, making those raids more interesting.