It's mostly any phase where the enemy goes first that the 0 cards became a hindrance -> since they play the anchor card, you're faced with a SPD of 1, making the 0 cards useless, if I understood the system correctly. It made the enemy phases always go - they play a card, I play one card - round ends. 0 cards were important, but only on turns where you pick the anchor, so having as many as I did slowed down what I could do.(I had turns where only one character had a card that wasn't a 0 card; perhaps that was an unfortunate luck of the draw?)
I do agree that one tutorial battle would have been a better demo to present, but yeah - hindsight. I still think what you have is neat!
Also, I forgot to mention - your writing is very nice. I wasn't absorbing much of it because I wasn't very invested in the characters (Just wanted to play cards haha sorry!) but stylistically your writing has nice flow.