Holy is an absolute monster in Aurum Vale. WHM absolutely has issues but for the most part using Regen while pulling and proceeding to Holy spam right from the get go is very good. If the tank is losing too much HP during Holy spam you can cast Cure 2 between the Holy stuns. If the WHM wasn't spamming Holy they were not doing everything within their power to keep the tank alive.

That said WHM absolutely needs improvements for low levels but trash pulls should not be that much of an issue at that point when Holy exists. If they were spamming Holy and the trash pull managed to last long enough or the tank still took too much damage than someone else was doing something wrong and other healers would have likely struggled as well.