That usually does it for me, you are given the tools to heal and DPS, but you have people whom are not comfortable in using them. Saving their swiftcast for a death that is likely not going to happen on a trash pull when they could use it on the holy to stun the mobs to not only do less damage to the tank but also eliminate the trash quicker.
The best mitigation in the game is actually more damage. The sooner the trash dies, the less you have to heal or deal with.
