Casters can get gap closed and stunned / interrupted into oblivion by mongo melee.
Melee can get kited to hell by ranged.
Hunters can't be interrupted and can't be kited (especially in the case of BM). A good hunter is a hard fight for any class, fighting a hunter forces you to play smart because you can't just chase him around the pillar and hope that you catch him before his pet mauls your face off.
As a consequence, people throw a shitfit on the forums because they don't understand how to fight a hunter and get them nerfed. Notice how whenever hunters do good damage they easily climb ratings and cause a ruckus on the official forums? With the recent nerf, hunters still have no mechanical weaknesses but now their damage is so sh!t that they might as well stop playing arena for this season.
Hunters need a mechanical weakness or other classes need theirs removed. Most melee can't be kited right but but I'm presuming their plot armor will last only until the next major redesign (hopefully coming next xpack). Meanwhile casters either need to be able to cast 100% of their abilities on the move (at least in PvP) or hunters need their deadzone back.
And yes, I'm a hunter. I want a very obvious mechanical weakness that people would be able to exploit to counter me. I'm tired of hitting like a wet noodle in PvP.