Another Idea:
Simply increase the chance of increasing either Leadership or the appropriate weapon skill each battle (with weapon skill increase being more likely). Make it nearly guaranteed likely that one or the other will increase.
It may sound extreme to virtually guarantee an increase in one department of the other. However, even if ALL skills increased by one after every battle, it would still take a LOT of battles to max them out. Something in the range of 80 of so. I doubt many characters have engaged in so many battles and if they have, they deserve the level of skill they gain.
Besides, skills would still degrade when unused so skilled warriors who start hanging out at their estates would see hard earned skills drop. Unless the use the Academy to keep sharp. Then Academies become a recurse for Skill maintenance primarily and serve as skill builders only when a good battle can not be found.
I honestly think I like this option best. Lead infantry for a while and see meaningful swordsmanship increase and lower, but still noticeable leadership increase. Switch to Cavalry and see Jousting increase a bunch and leadership some too.
Archer commanders may miss out a bit but that could just be seen as the disadvantage of commanding ranged troops with higher survivability rates.
