Speaking from a White Mage perspective, Cleric's Stance is like bane of healing. There are times where I think I've turned it off and will start healing, noticing people won't get anywhere as much HP as I think they should. Then realize Cleric's Stance never deactivated. So the gap in Mind vs. Intelligence is great, but the 10% damage bonus and the 20% healing penalty make a large impact later as well.

e.g. Level 50, Stone II does 280 damage without Cleric's Stance. With Cleric's Stance, it does 380 damage (roughly 35% damage boost).
Wasn't paying attention to the number on the heal, only to know, it wasn't sufficient to heal in a boss fight with it on (Stoneskin on the tank howe'er)...