When I'm a DRG, if I rip aggro off the tank (it happens; I use regular dungeons as a chance to build muscle memory on the full rotation so on even random trash mobs I will blow all my CDs as I would in something like Alexander), I'll just use Elusive Jump + Spineshatter/Dragonfire Dive to halve my aggro and get back into position. While the tank's primary focus is to maintain aggro, sometimes gear discrepancies, skill level or even something as simple as getting a few lucky crits can mess with that. Part of a DPSes responsibility is making sure to deal as much damage as possible while also managing their aggro output. As far as I know, all DPS classes have at least one tool. They need to use them.