I don't think GP is saying we'd have difficulty encoding the cards. I think they're saying that deck performance is very sensitive to minor changes, and dependent on a lot of interactions between sets of cards.
To add to that point, decks can be good or bad based on the ecosystem (meta) they're playing in. A deck that aims to rush you down might be great in a meta where players expect slow decks, but terrible in a meta where many decks have means of healing themselves.
