Thanks for taking the time to play and share your feedback!
I was hoping that auto-battle would be faster (10 to 20 seconds), just long enough that you could see observe how your deck build performed before tuning it further by buying new cards. Unfortunately, I didn't manage to create good ways to force a quick battle during the jam, so it was possible to build really slow decks! In fact, you're basically invincible if you just buy a ton of shields... but it makes the game super slow and boring.
A possible forcing function to make battles faster could be something like: the player takes 1 HP of damage per turn in battle. This would force you to build a deck that deals damage quickly enough, else you die!