I do agree that it's weird that main story trials and dungeons aren't synced. Especially Castrum and Praetorium. But that being said, the dungeons weren't designed to be speedran. If you want to do a speedrun, don't pug it... actually, that's an idea. Removing the level sync for premades.
Though I still disagree with the idea that you're being hampered by being forced to be "merely" overgeared for dungeons.