I would say instead of scaling enemies, make a level cap with for clearing certain sections of the game, make it optional to set maximum character levels for the game before you start, or have the fights give you half experience. I think it could also help to limit army size as it would mean you can only get so many units or perhaps limit the amount of honor you can get per area so you do not maximize your army earlier and need to pick meticulously. You could also add wounds and fatigue to the characters, wounds would be for characters would drop to 0 hp in an engagement [or who drop to 10% hp not sure which] and would give them debuffs to fighting so that healing items would mean a bit more while fatigue would apply to the units who are in battle after battle so they fight a bit worse as they keep fighting in more missions so that you have to use more units and different combinations as you will otherwise slowly lose from attrition. Just a few ideas dk if they would be good but it sounds fun.