It varies hard by class, too. I’ve leveled an 80 shaman and a 60 warrior so far. Doing Heroic world content as Enhancement, I was constantly somewhere between “barely able to kill a single regular mob,” and “can’t even kill a single mob” because the white damage was melting me in the space of a few GCDs. I eventually gave up and maxxed out queuing as Resto for insta queues and Call to Arms rewards, but even at 80 with full epics in the 590-600 range, I’m still struggling with world rares.
Meanwhile, the warrior is cruising so comfortably as Fury that I keep getting paranoid I’ve accidentally switched back to Normal world.