Fractal dragons isn't really viable anyway, so I don't think this is a problem.
I wish that was true so it wouldn't hit us so badly, but it's not. Fractal Bone Dragons in BoneBolt was one of the most versatile decks in War 3, and one of the best counters to both rushes and stalls combined (which helped a lot against Fire, ironically). With this cap, it will have a very hard time OTK'ing, which is disastrous for the deck type in general (includes all types of Aether/Light stalls).
I'm glad most Fractal decks don't need 50 quanta to work, but the cap has the potential to hurt them all since you can easily include a higher cost creature to Fractal in any Fractal deck to give it more stall-busting potential. This is extremely helpful in environments like War where having decks that can adapt is a huge advantage.
It would be smoother to nerf Fire Bolt directly, as the current cap reduces the amount of viable strategies in the game, making it less multi-layered and more RPS. If the intention was to nerf all pump spells, it would even then be easier to nerf them separately. However, if we get cards that can raise the quanta cap, the amount of strategies would increase right back again. I would prefer if it happened simultaneously as the cap, I will admit.
Well, I think there is something to be said about this though. I agree that OTKing with bonebolt won't be possible anymore, but if you play 5 Bone Dragons in one go, followed by another one next turn, you're quite possibly 2TKing and don't miss THAT much. In fact, since at BEST you're getting 8 dragons from a Fractal, you're missing out on 3 of them, without considering those lost to dead cards in hand (other fractals, for instance) or similar. I don't think it's quite that drastic a nerf, really. However, I believe you have more experience than me in the matter. Question is, are the benefits of having a quanta cap more than its problems?
Cons: Firestall isn't really nerfed (although new counters to it are now possible). Ice Bolt OTK is no longer possible, as is Drain Life OTK (but
gets Shard of Void). Stone Skin doesn't work well, but can be changed to work better with the cap. Dissipation Shield is practically untouched. Fractal Dragon decks are less effective.
Pros: we have a new toy to play with in card creation. Firestall got
slightly nerfed.
EDIT: I should note that I, for one, like the quanta cap. But I'm starting to think people complaining have a reason to. :/