Hero party was able to get so far b/c the tank was allowing them to be reckless by absorbing any damage they took. The hero mistook it as his own fortitude and blames the tank for losing his shield buff, "shell". I feel sorry for the healer, Nothing worse than having to heal the entire party and getting healing aggro as a result.
Now that he knows about his damaging skill, He can turn the damage he takes and reflect it back to the attacker, augmenting the damage of the party.