Most vets were happy when Zanz nerfed this from 10 to 9 scrambled quanta. It's no real nerf, but it's a sign of the right direction. As a single card, it's still too effective against too many decks of course. The popular previously proposed nerf was +1 cost, and it would certainly have a larger impact than lowering the scramble by that little, but either method works for nerfing if the right proportions are used.
My preliminary estimation would be that 7 scramble would be closer to balanced, but in honesty you can't fix the real problem of this card with either method; that it works too well against too many decks. If it worked well against a few, it would be no problem.
There's only a slight difference when you compare its effects in the unupped and upped meta, but it's certainly more potent on its own in the unupped environment. Unfortunately you mostly just see it in DBH-bows in the upped meta, and they're pretty decently OP.
Denial is striking at the basic needs of a deck; almost no decks work without quanta. Having that in the meta is fine, even if it might prevent a match from ever really happening, which kind of ruins the point for one involved party. Having a single card specifically designed against all non-rainbows, however, is not good for the meta. The same could be said for Black Hole if rainbows were more common in organized PvP and if it was as effective as Discord. Thanks to Nova, it's not.
I stand by my old opinion that +1 cost would be a big step towards balancing Discord.