The big issue here probably is scaling. Blizzard has been a long time opponent of multiplicative bonuses. One reason, for example, would be that if your gear increases your damage by 100% at 60, it will also increase your damage by 100% at 70. Author takes Critical Strike as an example of multiplicative damage bonus, yet Blizzard already implemented a system to reduce effectiveness of low level gear at higher levels.
Now, if we do decide to change +damage system from +spell damage to %damage, adjustable by level, such as the current rating systems, I don't see much difference between these two systems (well, there are some). And honestly, I'd rather prefer static +damage and at least do the same damage at 70 as I do at 60, rather than actually losing damage every time you level up if you don't buy a new rank of the spell, because %damage gear scaled back on me.
Now, a much simpler solution would be to make the cost of +healing lower, to the tune of 3:1 ratio with spell damage. Also, Stamina cost would have to be decreased even further - because greater healing power would result in need for higher DPS bosses, resulting in bigger hits taken by tanks, resulting in too many situations where meager scaling of health pool would not be enough to prevent 1-2 shots.
Now, if we do decide to change +damage system from +spell damage to %damage, adjustable by level, such as the current rating systems, I don't see much difference between these two systems (well, there are some). And honestly, I'd rather prefer static +damage and at least do the same damage at 70 as I do at 60, rather than actually losing damage every time you level up if you don't buy a new rank of the spell, because %damage gear scaled back on me.
Now, a much simpler solution would be to make the cost of +healing lower, to the tune of 3:1 ratio with spell damage. Also, Stamina cost would have to be decreased even further - because greater healing power would result in need for higher DPS bosses, resulting in bigger hits taken by tanks, resulting in too many situations where meager scaling of health pool would not be enough to prevent 1-2 shots.