For those who are having issues with not being able to fight the valiants on their racial mount. use the Quel'dorei steed. for some dang reason it works and you can complete the quest if you cant do it on the other mounts. ive managed to do the grand melee quest 4-5 times with the Quel'dorei steed instead of the Elekk (main is a Draenei hunter).