Well, one of the things is the dungeons are tuned so "average" players can clear it at the minimum ilvl required which for the new dungeons is 210. There's a huge difference between any player at 210 and one at 250+ not even bringing skilled players into account. The only way to make it "more challenging" (not really) while making pretty much all players able to play is enforce a strict ilvl sync. What would you rather have, super fast runs at 250+ ilvl or be stuck at 210 and have it take forever?