Holy crap miracles are actual garbage. I linked with a Virtue and thought his abilities were too good to be true. I swapped my gandayah's level ~15 ~40 magic ass for Virtue's level 31 100 magic ass and made him my new healer. I thought he would blow my gandayah out of the water with his 150 power heals + total debuff removal (Vitae) every couple of turns. Yet my first battle I went into with Virtue I noticed he was hardly doing anything. Then I noticed the exp based cooldown. Welp so much for that. That's what I get for deleting lifegiver gandayah. Also I'm playing a cunning mask so when I first saw Lux I thought it was practically a straight upgrade to Inquisition. It is if you're only going to cast either spell one time ever.
You get 1 (one) use of either miracle ability every 40% exp (20% with a passive ability). Oh and the cooldowns are linked so both of Virtue's miracles will be on cooldown after either ability gets used. Vitae barely gets a pass just because it's a pure gem plus a big heal for everyone, so it might be ok in a hard battle. Though in such a hard battle you might have to retreat and regroup (i.e. no more miracle), and also considering how you can't control when the AI actually uses it, I just can't advocate wasting an ability slot (or 3!) on those abilities. At least with Eternal Glory (which has a cooldown of NINE levels worth of exp) you get a full heal in the middle of a battle, possibly saving your special demon or even your entire run. Lux especially seems like trash, since you still have to roll to affect your enemies and once it's done, that's it, nothing left. You're stuck with 7 (or god forbid 5) abilities for the next few battles.
TL;DR Abilities with experience based cooldowns are trash.