As Lutine have said. Healing Bonus for wisdom is cap'd.
I would make two suggestions.
1. Reduce the amount of healing bonus on the items
2. Remove the healing bonus cap for wisdom and rework the healing bonus benefit of wisdom, so that you could gain more healing Bonus if you raise your wisdom, than statting like a tank
That would mean, that a healer will directly need to calculate if he/she wants more Life/Def or Heal.
It will be even more interesting if in future instances the difficulty is that high, that you need way more heal than the actual way to gear up and play your healer provide (stamina and def/hp stats, and high tiers OR boost your wisdom)