I’d like to throw in my support for a portion of your point 2..
You stated:
For example passive exp gain for low-level recruits even when in reserve…
I highly agree that in reserve, Battle Brothers should gain a small amount of XP per day. Perhaps 10, 25 or even 50xp a day, with maybe a larger xp gain in reserve depending on the difficulty level. I know that a Brother simply watching tactics unfold before them isn’t as valuable as being in the arena fighting, but still… I believe that there should be an xp gain in reserve.
"It is not death that a man should fear, but he should fear never beginning to live." ~Marcus Aurelius
Game: "Characters with a height advantage against their opponents are harder to hit"
Me: "That's not true, and my short axeman is living proof!"