Your argument is totally legitimate for low level dungeons, you just can't expect or count on nice hate holding tanks during low level DF experiences out of the lv50 dungeons.
But... I'm going to be extremely rude now, take care.
Sorry but for most dungeons 50 you shouldn't loose agro, just learn to keep hates better. The amount of bad lv50 tanks is truly impressing, it's even more sad when they are in the ilv100-ilv120+ range, what a shame.
You just can't ask your DPS to nerf themselves just because your tank is pure garbage, if he/she can't hold hate on pack of mobs as level 50 with decent gears, then the problem isn't your DPS but the tank. And so, the solution is simple

get better at tanking or change main job.