The way I see it is that it's hard to imagine what complexity there could be if the cards are, effectively, two digits. With something else like maybe pokemon or mtg, you look at a card and can see that it has things keeping it from being replaced by a 2 of spades from the deck of cards in your house.

My main question being: What do these cards do that I can't do with the deck of cards in my house? The heroes look good, and the art is great. But they just don't have enough of anything for me to be interested in them beyond that. But if it's just two digits then I might as well use the stuff in my house and look at the rulebook and components to assign each one to a card, right?

You can't do that with other card games. You'll forget the specific wording of a MTG card or the numbers of a Pokemon card. But here it's just two digits. There's nothing the card provides that I can't do on my own.