This is one more thread in which players in hardcore endgame forget that this game now has 70 levels and 340 something odd ilvls and not everyone are at the same stage. Sort of like asking ARR hunts to be level 70 and to hell with the people on-level, as though having a level 50 S rank spawn on your level 43 MIN isn't bad enough...
Yeah, dps can manage their agro against an undergeared tank, it's called sheathing your weapon. But between that being the definition of a dps loss, and it just looking bad, I think the ilvl sync is preferable. At least overgeared dps won't sit there and do nothing.
Then there's also the flip side. Think of an overgeared tank with newbie dps. How long before the tank starts complaining about parsing more than the dps, or stance-dances into dps stance only to see the adds don't die fast enough and they run out of cooldowns and die and they complain about the dps?
Yeah, it's on them, like LalaRu said. But it's still a trash experience for the rest of the party.

Let it also be said that 'it's in expert roulette' doesn't mean anything. It's the hardest content for most casual players, and hey, guess what, those won't have 340 gear because casuals can't upgrade yet. So why don't we keep that in mind and accept who that content is actually for in the first place. Wait a week and you'll have your Ultimate Bahamut to go in full ilvl against, leave the dungeons for the people they were meant for.