Why does Revitalize not improve Dr. Mundo's R and passive healing but Grievious Wounds reduces it?

Mundo's self-healing is classified as health regen, which Revitalize does not affect. Grievous Wounds affects all forms of healing including health regen.

I agree, the wording could use some cleaning up. It's also really frustrating that it doesn't actually make heroes like Pyke or Tahm Kench get any more healing, either. It just makes them heal faster, for some reason?