You can't balance a pool of 3000 cards. And it's not about balance even, it's about variety. You can't keep printing better and better cards, the powercreep will be absurd. It already is in this game. The way they introduce new decks is to make old decks redundant. Where is your OP Daria Rune now? It was the shit 6 months ago. Not much has changed with that deck but everything else can vomit stats better and faster now. That's horrible game design. If they don't print better cards, people will just play the old powerful cards and it will be hard to make newer stuff stick unless they're just strictly better... They said they're changing their direciton, we will see.
Just going and changing and ruining old cards people like is bad too. That's why we have formats in card games, it's the cleanest solution. Somebody likes playing dshift, they should be able to, just not in the main format forever.
In case of this game, I think they haven't really tried to truly introduce brand new decks and strats. It's been mostly about cheating out absurd stats in some way as fast as possible and every class has that now. It's not interesting. They need to try to be more creative if this game is to last for many years.
The only really different deck than the rest is probably earth rite burn rune deck. I like that deck, it probably takes the most brain time to play in this game, probably why it's not very popular despite being good lol. Everything else is same shit. Sword is dumbest garbage ever with ambush and storm. Who enjoys that? Neutral decks are probably the laziest bullshit I've seen. Cmon, who got paid for designing that shit or pre nerf blood. lolol. Haven used to take some skill and foresight, they ruined that too. Dragon is maybe different but it's still so dumb. The game needs more complexity, it's too easy and simple to just curve to victory. I used to shit on hearthstone for being too basic and simple, but this game is even more basic that that. HS actually is trying to add complexity slowly.
They need to try harder. I agree that the problem is not too many card yet. It's probably soon for that. The problem is bad design.