I don't remember this being mentioned, so forgive me if you've heard this countless times before. While spoiling as little as possible, what exactly is the in-story justification for being able to save Hector?
The explanation for being able to save Hector is that the prison he's being kept in is visible on the map, and you have xth amount of turns to reach him. Even then, healing magic is not time magic, you can't "Undo" all the shrapnel, the melted in stone that's merged with his flesh, the arrowheads and the bone fragments. One would need a masterclass bishop and surgeon to 'save' Hector. What you have is a novice cleric, an arcanist, a noble girl on a horse and a slacker monk. None of whom can really do more than help keep the comatose cadaver alive as best they can while hoping to get him to someone who can truly help.
Something else you could do with the fatigue system is making fatigued units miss more often and make them use up more weapon durability when making an attack, and it's easily justified because as they are getting tired from constant battle,they would be making more and more mistakes in battle.
Edit: adding this on because I just thought of it - maybe removing their weapon advantage because as the characters are getting tired, they can longer exploit the advantage their weapons have.
This is miserable. The idea of fatigue is not for it to be miserable, it's to be easily understood, with very clear cut features that affect a unit more the stronger that unit is. That is the 'genius' of Fatigue, by the way, that if a unit is weak, then Fatigue doesn't really 'do' anything to them. But if a unit is overly powerful, then their negatives are far grander and debilitating.
What if prepromoted units and old characters like Karel and Jagen get fatigued faster? Makes sense and also enables them to be stronger than other prepromotes while also keep them for becoming must-use for the player.
Then it'd be an unreasonable and unnecessary debuff along with adding more information the player needs conveyed. Here's a quick lesson in UX design. A user should understand at a glance what it is they're looking at. There's a reason Fatigue is planned to be on the Portrait-side of the screen, so the player can always track it.
And you know? I won't claim it'll be right the first time. That's not possible. There are going to be things we have to tweak, whether it be how much EXP units gain, their growths, the overall level cap going from 20/30 to 30/30 or whatever lies in-between. I have to test that out. But like with the removal of weight, I'm pretty confident in the overall system. Of course there are going to be tests that need to happen, what new system works out the box?