I understand the idea of perfecting the difficulty you already have. That makes sense.
When I design games, I try to optimise for fun over realistic and pure logistics. When I played the game I found the angel/devil fight super annoying because I lost a really good run. If the solution to the fight is what I think it is, then it is just too unlikely to win to be worth sacrificing that much cargo unless I'm in endless mode.
Being able to opt out of fights is rare, I agree but it doesn't help that I have no clue what I need to do to win. I like the skeleton fight because it gives you the option to fight, and you can see what you're up against. I mention a potential solution below.
When I talk about rigging the dice, I also see why you wouldn't like this idea. I mainly want the first dice roll and maybe the first battle to be rigged. I restarted too many games because I didn't roll higher than a 7 or encountered a *6* as my first enemy.
If you want to keep the mystery of the game, perhaps add a log book which could double as a statistics page. This would be where some information about certain events would be kept after you encounter them multiple times. Or you could do a *secret notes* type thing similar to stardew valley and finding notes that tell you certain loved gifts. Adding a log book allows some information to be retained over different playthroughs and acts as a trophy collection or a secondary objective for players.
I really enjoy discussing game design, if you want to go more in depth.