BS. There are hunter counters. Hunters are just so taboo in this bracket that everyone who dies by them insist that they can't be killed.
Hunters do insanely more damage than any other Class at 20, making them the very best DPS by far, with more than enough utility as well. The only reason to even fill a DPS spot with something other than a Hunter, is for hard CC (Fear, Polymorph, etc), or a Rogue for EFC 4+ Stacks burst
There's simply no other Class that can compete with the damage output of Hunters at 20. To add insult to injury, Hunters can also kill every Class 1v1 pretty easily. The only things that will give you trouble are Paladins and Priests that stand there healing themselves, but at that point you've effectively locked them down anyway, and they'll die before too long
Conc shot Mounted people and immediately get a free kill, Conc shot anyone out of position and immediately get a free kill, Conc shot any Melee Class and immediately get a free kill. There's also a laughable room for error, when you can Conc shot, Scatter shot, Disarm, and Disengage your way to safety, if you mess up
There's just nothing that can be done, when you call a target, and 5 Hunters Explosive Shot it. That guy is f***ed, and then it's onto the next DPS who's going to die in one to two globals from Arcane Shots. The team with more Hunters will win, unless they're so terrible they aren't using a voice chat