Thanks for your comment lightdisk. Sorry this reply is so late lol - I guess I'm mainly making it for the benefit of anyone else reading.
My intention with the mana system was to incentivise using WP skills to restore JP, which requires a bit of strategic thought (e.g., hitting elemental weaknesses for more WP to use Trumpet Blast or Leech Blade). The second part of this is that out of combat recovery should be primarily done with items and only spells as an absolute last resort, to conserve JP.
I can get if this wasn't very clear, or if it was clear but you still feel it was harsh. My goal was to emphasise the chronic resource depletion aspect of dungeons as a source of difficulty, while also making mana a meaningful resource as opposed to 'spam til you're out'.
I know I am super late with this reply but I would definitely appreciate your thoughts on where this went wrong. Thanks so much again!