Okay, I rage-quit and uninstalled it because enemies dealt +1 more damage than their sum was going to be, causing me to die when I had intended to go to 1 HP to maximize a health-restoring tome. I didn't understand what caused them to deal greater damage. I wish the game would preview how much damage you'll receive if you just ignore enemies and keep unveiling cards.
The Weakness rebuff doesn't say exactly how much weaker you get; it should be clear that it causes -1 ATK with everything, or actually reduce your cards' values accordingly. The game really needs quality-of-life features and clearer wording in its descriptions.