It doesn't have to do twice the damage. Make it 50% and that would still be awesome. I think it would bring UD back up a notch.
I don't think so, since there is turn delay on temple so you can't surprise anyone with it - if you were playing a DE deck and temple was out you'd know to leave AP. I guess mindstorm exists but that is a lot of nora for the combo. I'd it proved a problem you could make it 33℅ or 25℅ - whatever, it's still better than having a banned rune.