Thanks for the feedback. We wanted to add more, but ran out of time. The core will still primarily be choosing which item to consume, but have a bit more strategy based on the enemy. We are debating on what kind of indicators/clues to provide about what the enemy is planning, along with more info on the enemy's strengths and weaknesses. Certain items will also have short and long term effects, such as leveling up your stats for the rest of the battle, or even permanently.
I turned on debugging, and it does look like the defend logic is working. It is a set multiplier to the final damage amount applied right before the character takes the damage. Several attacks have a high variability, so that may be why it seems like it is not working. We will look into options to better convey its effectiveness.
Thanks for playing!