Hello!

The healing increase is based on the original value.

So, if the original value of the skill is 20% and you upgrade the skill to give you 30% additional heal, it will increase by 6%: 30% out of 20% = 6%
As for the cooldown case, it should not work like that. Please send us more information about this case:
1. Hero name
2. Skill name (is it divine light only?)
3. Screenshot of the skill

Sorry to somewhat pull this out of the crypt, but I'm adding onto it because it somewhat frustrated me to come across this situation.

The problem at hand is that Warpriest's 'Divine Light' ability simply gains a two-turn Cooldown upon level 3 Awakening with zero warning to be had, other than paying sly attention to her maxed stats in the compendium, which I did not catch until mid-fight after Awakening her.

So far, no other Champion I've upgraded has had a skill increase in CD, and their starting CDs match their Awakened CDs in the compendium.

So yes, the level 5 'Cooldown -1' is technically working, but it's extremely frustrating to have boosted her via items just to discover a hefty fine that I was not at all expecting in the form of that +2 turn base CD; I would have happily left her Unawakened for a 2-turn single heal instead of a 4-turn AoE.