Just tried that on my level 82 hunter. You need to atack the small mobs first to even get exp, I did that with trap launcher + fire trap. 4.5k per little mob = 13,5k exp for 1 tank and it took me 30 seconds to kill one and the respawn is not that good, you often have to walk a lot but lets say im unlucky/i kill them to slow so you kill 2 tanks per minute = 27k exp/minute
27k exp/min * 60 = 1.620 million exp/h and we need 4m exp for 83. Either it's fixed or I dont know it's not worth to level like that.
Ps. I'm in heirlooms + lvl 25 guild