I think the training is too fast, at the moment, for realism. How can a peasant be trained, even with the help of a couple of battles, to the level of a man-at-arms, (that's a professional, full-time fighting man) within a week or 10 days?
It should, realistically, take months.
And archers - it takes years to develop the physique to handle a longbow with 60 or 80 Kg.s draw. Yet the game takes a townsman, or a random 'village lad willing to seek his fortune in war' and within max. 2 weeks, if they are still alive, they are wielding longbows!
Maybe the game needs to assign some attributes to low-level troops, randomly, and make training a much longer-term thing. The randomly assigned attributes would allow low level troops to hold their own if used effectively: For example, Swadian recruits might be given +3 in powerstrike, or +100 in 1-handed-weaponskills, or +(1 Strength and 50 Crossbow) to reflect the national tendency towards strong melee troops and crossbowmen; Khergit recruits would be assigned at random from +3 riding, or +3 power draw, or +3 horse-archery, or +100 archery - to reflect the national tendency towards mounted archers,
Obviously there would need to be a mechanism for identifying what your recruits were actually good at, and then using them accordingly (ie, choosing the right upgrade path when they were eventually upgrade-able).
This does move away from the question of the training skill a bit, but it's something we created in a mod a while ago, namely that after the first 24hours with your party, 'recruits' (we used 'villager' for every culture) are randomly swapped out for specialist recruits.
the script (paraphrased) was
count number of trp_village_recruit = x
remove x village recruit
get random in range (village rogue, village smith) 'new_troop'
add x number of troops 'new_troop' to party
the range 'village rogue, village smith' included a rogue (skirmisher-skill) a stable-hand (horse skills) a labourer (infantry) and a smith (infantry)
so your initial recruit had a 50% chance of being destined for infantry life, and 25% each chance of being suitable for cavalry or skirmisher work.
The troop level didn't increase with this change, but their attributes did, to reflect what they were good at, and the potential upgrade paths also changed. The script ran every 24 hours, basically on the assumption that after a couple of meals & beers around the campfire, any new recruit would have spoken out about what he used to do and be...
I know some people don't like this system, because it smacks of fatalism (once a ****-kicker, always a Swadian Crossbowman)
but for us, it works, because it allows the upgrade tree to branch off at a much lower level, it gives low-level troops a useful specialisation very quickly without making them supertroops, and it means you don't have the unrealistic situation of every recruit being suitable for heavy cavalry (or whatever other specialisation).