If you dont want dungeons to be a snooze, just dont run them unsynced!
There is no dungeon in the game where you can be 100 or more ilvl's over the min one without unsyncing it.
What could be done is sync most lower level dungeons just a bit lower then they currently are.

You say grinding hardly exists in this game?? then you propebly never done any relic when they were current. the grinding was real. Case in point was the arr atma grinding where people would take months to get the necesary crystals. or later on when we needed a semi rare dungeon drop from the final boss, leading to some people having to run the dungeon like 50-100 times.
and that for 12 drops in total