Something i would like to give you kuddos for: and i don't know how you thought of this but its pretty clever;
in darkest dungeons, the player can just play the same dungeon over and over to grind newer level parties. In your game, every dungeon clear removes that dungeon: you cant play it anymore for grinding purposes. BUT:
When things get too difficult, you can do the rescue girl quests to get resources to upgrade your base, which means you can just BUY better heros! pretty smart. Although this does make doing the personal quests a little tricky . I guess thats on the player to plan ahead!
Cool mechanic tho