Yikes! Blinding Angel was never this easy to trigger. Admittedly also not this double-edged. Looks like it'd be terrifying in a mill-based deck, a ping or burn deck, or a TurboFog-style deck. Scary.

Wow. I remember when Relearn/Orim's Chant decks were a thing. Player had to really fight to Orim's Chant every turn. It was good, but it seemed fair.

This, on the other hand, seems far too simple. To add insult to injury, I assume that the spell you will most likely cast to prevent attacks for the turn will be Cancel, in response to the opponent's creature kill.

The double edged thing, doesn't really seem like a thing. Just don't build a deck that relies on attacking to win. Turbo Fog decks generally win through Planeswalkers anyways.

That's somewhat better. Casting two spells on your turn every turn is significantly more of a hoop to jump through than one. It's still eminently achievable with things like Crown of Flames, Mark of Fury, Mind Games, Petals of Insight, Hands of Binding, or just Howling Mine / Font of Mythos and cheap spells; but it needs a little more work, so this is fairer.

I do still wonder if the reward could be something other than preventing every opponent attacking, though.

Well... if we're nitpicking, it would make a lot more sense if the spell just made it so you couldn't be attacked until your next turn. After all, it only takes two players in an eight player cutthroat game to cast two spells per turn, for the combat step to be shut off for everybody.