For many players the overabundance of super knights is an issue and unrealistic.
In order for it to be realistic, here are my suggestions for Catholic factions (not all items will be moddable, I know):
Raising the troops
- King's Authority rating affects the type, number and "hiring cost" of knights available in the recruitment pool even with all required tech (quite often the barons wouldn't come and fight for a weak/despised king); so a king with low Authority would only be able to recruit the lesser, poorer nobility (those with something to gain) and not the élite troops (those with a lot to lose). A king with high Authority would be able to get the best troops available at the time, and more of them, for a lower cost. This raises the importance of role playing your king and heir and paying the price for poor leadership.
- A Governor's Loyalty rating should also affect the number and type of knights available in the recruitment pool in a given castle (low loyalty means low effectiveness in convincing the barons to fulfill the vows of their vassalage, whereas the lesser nobility may fight); settlements without family members should not be able to recruit knights, so your best and most loyal governors would have to ride around the kingdom mustering the best men available;
- High Authority and high Loyalty reduce "hiring cost" of knights (as they fought in exchange for land/title/semi-autonomy). Having low Authority and Loyalty means not only a decreased unit pool, but also higher cost of the knights who do make themselves available to fight ("If you want me to fight, make it worth my while. As it is, you have no authority over me so why should I care if you call on me to fight for you.")
- The level of land development and base farming affects the type and number of knights available in the region. A rich region (in which the king has invested significant funds in land improvement) would have several rich barons and many lesser nobles; a poor region would have perhaps only a few units of lesser nobles available. Why build a citadel in a poor region with poor farming and few nobles to assert authority over?
- An Armourer should be required in order to recruit any knights that have Partial Plate as their minimum armour, regardless of the other buildings you have (unless you mod in weapons and armour resources on the map in places like Toledo and Damascus and have a Merchant on those resources);
- The king's Piety affects his access to Order knights. Even if you have the Chapter House, why should these holy knights fight for a man who doesn't believe in God? You get 1 Order unit for every 2 Piety rings the king has and 1 unit for every Cathedral in your kingdom, 2 for every Huge Cathedral. So a low piety king can build Cathedrals to increase piety and access to Order Knights, and this legacy remains after his death, because Order Knights are still "attracted" by the Cathedrals themselves.
- After the discovery of gunpowder, all élite knight availability should gradually decrease, to as little as 25% of actual, representing many knights' refusal to fight against untrained peasantry that could kill them quite easily and where martial prowess and class mattered little.
Maintaining armies of knights
- Historically most knights fought as vassals for their feudal lord, creating a hierarchy of princes, earls, barons and lesser nobility. But they served for limited periods of time, so this should be reflected in the game. You raise knights when you need to go and fight, and when their period of service is up, they go back home (except for Crusades which have their own rules). For every turn beyond their base "availability period," their maintenance cost goes up in inverse proportion to the king's Authority rating. A high Authority king commands his vassals to serve beyond their agreed period; a low Authority king has to buy their continued service.
- Knights should take longer to become available again in regions, representing the time that lapsed between periods of service to the crown. This way regions can produce "waves" of knights over several turns, but knights with a sort of "shelf life," after which their maintance costs can skyrocket if you don't disband them (which can only be done in a friendly region, and you assume they find their own way home).
- Maintenance costs should be higher to represent the entourage and support required for these élite troops.
The effects of this approach:
1) you get realistic armies without oodles of super knights
2) your ability to raise and keep knights realistically comes from a) the wealth of your lands; b) the reputation and abilities of your monarchy
3) you can't prosecute long, unprofitable wars without draining your manpower and wealth
4) the sooner you develop professional armies, the better
5) mercenaries (including displaced/disenfranchised nobles) will have their rightful place in the game, especially élite/experienced mercenaries in the late period after the peak of the era of knighthood
These changes would make it extremely hard for a young and/or incompetently spineless ruler to run a vast empire, as it should be. In my current game as England my king got assassinated in Jerusalem after a Crusade. The 26 year-old successor has very low Authority, no Dread, no Chivalry, yet the kingdom still holds together and the lords still come to fight for him by the thousand without asking even a penny more for their loyalty. Historically this wouldn't have been remotely feasible before the Parliamentarian reforms of the late period which saw more organised government and the first inklings of nationhood.
In order to advance realism, something must also be devised to represent the barons' desire to keep fighting wars that were profitable for them (even against the wishes of the king and the Church), or they should revolt when the king insists on continuing unprofitable wars.
So perhaps making peace with a sworn enemy (predetermined in the diplomacy AI) causes unrest in regions where your high level knights come from (like it did when England tried to make peace with France during the 100 Years' War). And continuing an unprofitable war (read "unpopular with the barons") should also increase unrest in regions where they come from (i.e. where you have "knight producing facilities"). This increases the chance of rebellion from the barons who want things their own way.
Right now there's a mod called Road to Jerusalem which tries to allow for fewer super armies out by making knights "spawn" at fairly long intervals and making them cost more to raise/maintain. You have to wait quite a while for the unit pool to be full in a fortress/citadel. It's a workaround for the issues of cranking out knight-filled armies, but you still have to "suspend disbelief" in order to digest it properly.
Perhaps the above suggestions are already being considered by this mod?
