Your assuming a reasonably balanced game. There are plenty of examples where card games Basicly* just had one winning solution at some point. Granted, these types of games tend to be fairly fluid as new cards are added all the time.
*aka, there was a type of deck that is dominate even if it allows for various minor changes within that theme.
True, but in practice Hearthstone has been relatively balanced, and allows for a lot of different winning strategies that are all competitive. Right now I can think of at least seven very different decks off the top of my head that have been really popular in the last couple weeks, and it's pretty common to see people hit the top ranks with totally new deck ideas that nobody has seen before.
It's possible that tomorrow someone will find a game-breaking deck that beats the pants off of everything else out there, but it seems unlikely. The thing is, the game is somewhat self-correcting. The more popular a certain deck is, the more other decks will evolve to counter it.
*aka, there was a type of deck that is dominate even if it allows for various minor changes within that theme.