Actually, in my opinion, the current solution in the dungeons is trying to cater to both the speed runner and the player that just hit the item level requirement for the dungeon or someone new to the dungeon.
It's a fair middle ground.

If you make Trash harder to the point it is a challenge for ilvl110+ players, you must raise the level cap, which is not inline the ilvl 90 drops in there.
The other solution would be to reimplement the levelsynch to High level and Expert dungeons and have a challenge, so that you can see the dungeon is not too easy, you are just way too overgeared.

You just cannot make every one happy.
tbh, I hope you stay unhappy in this regard.