Yes DH has no healing. A guardian can make 8000k self healing to himself.
As soon as you left healer or your healer dead , you need to go graveyard all the time to get heals with dh.
If they decrease guardian to 30% health ,its just 6 seconds to get 100% health for them again. They are just slow.
I have a friend who started to main guardian druid 8.1 patch. He is rank 1 player.
He tells how can a spec be bad if something never dies on the rated battleground.
Leave healer or let your healer die and see what happens to your dh.
Also you can solo entire middle allliance/horde raid on deepwind gorge with guardian until healer reaches you.
DH is good with high mmr teams. Its the best on high mmr.