What if "pure" healers had a slightly higher base amount of healing then barrier healers but augments them by HoT while "barrier" healers had a slightly lower base amount of healing that is augmented by damage reduction instead of straight up damage negation?
You could still have damage negating barriers but as capstone abilities and pure healers would have burst healing on their capstone abilities.

For future healers, I would love a non-casting healer. All our healers are magic based.