Applies Grievous Wounds for 8 seconds if you are under 35% health
Physical damage applies Grievous Wounds for 3 seconds.
Physical damage applies Grievous Wounds for 5 seconds.
Damaging this person applies Grievous Wounds for 1 second.
The only one that's long is Morello, and it's gated by lowing the person to that health before it even procs in the first place.
And shields really don't need anything to counter it because they are a 1 time thing that disappears after a few seconds. Someone could give you a 3000 hp shield, but that's completely irrelevant if they use it when you aren't taking damage. Whereas healing is there after the affect has worn off.
If you are 200 HP and I shield you for 100 HP, you have 200 HP after the shield wears off. But if I heal you for 100 HP, now you have 300 HP, so my heal lasts longer in a sense.