Dragons are good, they ignore several types off cc with their HP and getting them to stay on the table for more than 1 turn than the first makes up for the cost. They bypass most shields with little loss. Dragons are often used for the last hits, their only real problem is antimatter imho.
Dragon are not bad but you shouldn't really use more than 3-4 in most decks. Few can muster the quanta to actively sustain and drop them every turn if need be.
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re: comparison of 2 frogs vs 1 dragon
It is important to realize that card games are all (really, all) about card advantage. The most powerful cards are ones that destroy multiple cards of your opponent (quicksand, pulverizer, etc), counter multiple cards (ice shield) or generate faster quantum so that you can play multiple cards faster than your opponent (supernova).
Dragons are powerful in that they are a lot of damage in one card. In this case, a dragon is worth 2-3 frogs.
Card advantage is not as important in this game as quanta acceleration. Being able to get quanta fast means using your stuff earlier and winning sooner, only because creatures attacks at once with no waiting and spells and their effects resolves at once (direct dmg) and cant be manually countered.
I hardly ever win a game where I get 2-3 pillars in tournaments and OFTEN not drawing a pillar for 2+ turns. I'm sick and tired of getting behind in quanta as that is the only reason for losses.
And don't talk to me about inferior deck building its insulting, I know hypergeometric probability and QI off the back of my hand.
Its all about luck.