I guess your definition of overgeared is different than what mine would be. The instance takes basically an hour to full clear (including Nightbane, and the time it takes to go back and kill the other bosses). Considering they are splitting it in 2 parts for 7.2, one four boss section shouldn't make it a longer instance than Halls of Valor.
It's a great instance though. Amazing for gearing up if you aren't deep into heroic/mythic raiding. Otherwise it's do Nightbane and/or hope for some good WF/TF loot from the instance. The chest pieces from nightbane combined with the trinkets through the instance make for some really powerful loot (eye of command, curator trinket and shade of aran trinket are all amazing trinkets respectively).