He had a point though. If this card is such a 'Rainbow Killer' - why then is it limited to Gravity? Shouldn't other Mono decks have an equal/or at least some way of battling a Rainbow Deck.
I think this card will see an initial grind-fest and then it will slowly drop out of favor. While the healing effect it gives is good, you would ultimately have to cast it when your opponent has 3x of each Quanta, giving the maximum possible 36 health returned. You would have to use pillar denial, such as Earthquakes and Deflagration/Pulverizer to make the most out of this card. And as such, this card will 'only' feature in Gravity/Earth Duo's or the adventurous Rainbow player. As said before, the true strength of this card lies in getting it 'and' casting it early on (perhaps with Precognition) to stop your opponent from getting the quanta he needs. It will, for better or for worse, add a new dynamic to pillar denial decks (prior to this card they had very limited ways of removing the Quanta a player already accumulated - Supernova's etc.)