The point being made here is troops gain xp without battle just very slowly and one at a time. As op said training 1 single recruit without battle takes about 20 days. Thats sort of ridiculous and it needs to be made more like warband where training is distributed to all soldiers under your level. On top of that the XP given through training needs to be increased. I by no means expect warband fast but I expect it to be at least possible.If the troops are supposed to get the XP they get when we simulate the battle in manual battles, than we shouldn't need a XP boost, but just a fix to the bug that makes them get less XP when we manually fight.
I do believe that this is the source of the problem. Check this out: https://forums.taleworlds.com/index...anual-battle-experience-is-unbalanced.407269/
As far as the XP gain from battles that also needs to act similar to warband in that xp was gained from being in battle and not just given to the ones with kills. If this happens your forced to choose between upgrading yourself and or your army. This is why OP said this sort of ruins the player progression. On top of that running around fighting looters just to upgrade your troops gets boring very fast.