In a pick of Laurion Inn, everyone in my group using the hotkey / main is assisting a mage pet in another group that was designated as main assist in his group. We nearly died over it.
The forums are filtering out the word @$$ -- the first 3 letters of /assist when used by themselves get sniped away. You can /assist main, or you can /assist Soandso -- both will work.
The present expansion has a multitude of bugs. The pet was tanking, Xianxu. I am a dumb warrior and some mistakes are to be expected, but still our group was using /assist main and it was getting a mob halfway across the zone.