I think DK healing is perfectly fine and viable.
Obsidian Shards is like Funnel Health, healing by damaging.
Igneous Weapons increase party's damage which is good.
Shattering Rocks is a very creative ability but no one really uses it. Idk why. But it makes your enemy's next attack heal their target. Which i have never seen an ability like this in the game. Very unique.
Cinder Storm is also very good. Heals allies in radius and reduces enemies movement speed. I think its a very useful ability.
Cauterize is very unique like Shattering Rocks too. It provides healing to an ally every 5 seconds and, the best part is, it scales off your maximum stat which makes this ability viable for every kind of build. Its a great support ability every DK should have in my opinion (if not went with Flames Of Oblivion morph)