20% damage reduction + 20% more healing gives better healing efficiency than 20% more healing + 15% more healing.
....and thats ignoring the fact that the PLD's version is actually 10% stronger.
If you cannot use it once every GCD, then it technically does have a cooldown. The cooldown is variable, but it still has a cooldown.
And using it twice in a row sounds great, except the PLD's cooldowns last longer than 2 GCDs.
