Just finished the sketch and I agree with your notes on not quite finding the ideal work around with Jusztina's AI (i primarily found myself in Persona 3 FES mode thinking oh god oh geez please dont waste MP anytime she would G-Cast a singular target).
Marie's options felt practical, though the most optimal I found was Misdirect vs a single enemy. What I enjoyed most was the atmosphere and gradual attrition of the fights as I began to notice mistakes in turns would later cost me in precious MP resources (where I only made it to the end in the last little stretch by spamming escape and praying after the earthquake(?) cutscene)
Enemies were nicely telegraphed with what they might do, the lizard being an interesting Red Mage fake-out, and I only ran into the Minotaur once but long enough to see Intercepting attacks not work and causing a decent amount of panic. I would have liked to see the minotaur a bit more but I'm not sure if having enemies that were immune to certain defensive tactics would have helped or harmed the experience, I feel that presence if it was more common would want Marie to be able to act twice (beyond RM2k's scope of course) or perhaps having two Marie's present (same moveset, but the potential to double action) could be interesting? Though that may lean more into puzzle battles with cut and dry solutions and cost a little on the attrition, unless maybe HP/MP were split equally between the two Maries leading to two princess shields that you have to watch the individual resources of while still keeping the princess afloat. (Traditionally speaking one should probably block phys and the other block mag but I really the idea of two equivalent movesets that the player can optimize with the turn economy in mind)
I also think giving Jusztina the option to act before certain enemies would be nice too, especially in battles that mix enemies she can and cannot act before (though with current balance she would just delete the enemies in the first part of the dungeon lol so that might move away from the vision rather than aid it)
Idk, I liked the concept overall and I'm glad I finally sat down and played one of your sketches!
Wish you the best with your next idea and steady recovery from burnout!