Fast yes, but I think you could make it faster!
- First and foremost you don't have any weapons. Longswords will do 7 damage for 1 quanta, even if they only last a couple of turns that's a nice damage boost in a fast deck. You could consider Fahrenheit but it's probably not fast enough for your deck. Additionally your cremations will generate non-fire quanta which the longswords can use.
- Are your phoenixes pulling their weight? They cost 7 quanta but only do 7 damage. Would dragons be a better choice?
- I'd say you're destroyer heavy. You're not generating enough quanta to grow more than 2 destroyers so 4-5 should be plenty for the deck. Admittedly they are a good quanta:damage tradeoff, but dragons / minor phoenixes might be better depending on whether you generally find yourself long / short on quanta.
The weapon idea is one I played with and I think it would be useful against decks with a lot of creature control. But I find that everyone has permanent control, and I don't want to have it stolen from me and possibly have to blow it up. (explosions are in here for shields primarily).
The destroyers are a must, they are very easy to get out first turn. I can often get 2 of them out w/ 2x cremation minor phoenix, brimstone, or 2x tower, brimstone, cremation, or best of all, 2x cremation, 1 tower, 1 phoenix, 1 brimstone (plus 2 destroyer in each case).
I can grow them both because cremation gives 1x earth quanta when i use it, sometimes i'm using two cremations to get to my first 2 destroyers. So I can grow them both through 2 or 3 turns... this deck kills in 4 to 5 turns with a good draw... so who cares if i can't keep growing them indefinitely?
Dragons would slow this deck down BIG TIME. Too much cost, cant get them out first turn, they don't grow. I can see a particular situation where a deck with dragons would kill faster than this one, but that deck would not do it consistently (the above deck is consistent).
Phoenix is in here to make the deck viable. Lava destroyers are vulnerable to all kinds of damage spells, phoenix can usually live through all of that stuff. Not to mention phoenix / minor phoenix work well with cremation.