Doesn't really matter in the eternal formats, worst thing you can do with Temporal Mastery is pitch it to Force of Will. Standard, Modern or whatever there's major upside to running at least one copy. 12% auto-mulligan, rest of the time I get Time Walk? With a card that good, I'll take my chances. Straight control decks might even run multiple copies, since they actually plan to make it to the point of being able to hardcast the things (not ideal at 7 mana but hey, a free turn's a free turn). I don't think Miracles.dec will be a major player, at least not in Standard, but god damn what were they thinking?
Thunderous Wrath isn't all that great. Even at the Miracle cost, sure it's pretty efficient then but you still don't get to choose the optimal timing to cast it like you would a typical burn spell. Bolt your guy in response to equipment, in combat, your face end of turn after I realize I don't need to kill a dude with it. There's no opportunity to gain tempo off it and it's overkill on most early-game creatures anyway. It's more like a big Rift Bolt that has a chance of showing up in your opening hand and being horribly inefficient, or even just showing up early and ruining your curve (Turn 2 Shrine of Burning Rage, etc.) by obligating you to spend that R when you might already have plans to spend all your mana.
