I have run with groups that took almost as long to kill the rock add as it does before the next add spawns, which means VERY little time on the actual boss (but the tank) and it can take way too many adds. Now does this mean they will not finish the wall? well recently it does seem this has been an issue and I can see why the tank may have not wanted to waste 15min to get to the wall if he truly did not think it would be downed, although I personally would have at least tried and worst case replaced one dps when it wasn't working hoping for a better dps to take out the wall.