Archangel is not so strong that your opponent will avoid killing this card just to prevent it from turning into one. And if you buff this card (blessing, butterfly effect), it's not too different from buffing, say, a micro abomination. That completely ignores the point of this card - high cost for ability to transform.
I get where you are going with buffing this card so that the opponent will have to choose, either leave it powerful as it is or waste a CC only to have to deal with an archangel afterward. But it still just seems like a waste of a butterfly effect that could actually be used to destroy permanents rather than gain you an archangel.