For something like a deck building game, if all decks are viable (competitive) then there may as well be no deck building component. In fact a game like that is

For something like a deck building game, if all decks are viable (competitive) then there may as well be no deck building component. In fact a game like that is probably a pretty muddy brown color in terms of card variety. That would adversely affect the business model of selling new cards as well. Desirable qualities in a game in terms of how it is balanced are way more complex than just every option being viable and leading to an even win rate against a similarly skilled opponent.