Does anyone find automatic recruitment of cavalry from castle weird? No stables perequisite needed. and for comparison you'll need every upgrade of barrack line of buildings to get the infantry you wanted. I have modded the export_descr_buildings.txt to fix this problem. Under the fixer (tested, works fine), Every cavalry unit except the most basic ones require stable line of building.
For instance, Motte and Bailey no longer offer any cavalry, nor does the Wooden Castle, the Castle only offers Mounted Sergeant level of cavalry (Hobilars, Scouts, Border Horse, etc) and up to Citadel only so. every other Horse units require a stable line of building.
Also, the Castle will provide low level infantry at a low rate. e.g if you don't have a mustering hall within a Castle, it will still provide peasant at around one unit per five turn rate.
The mod took into account the traditional horseback nations of Turks, Russia and Moors, their Castles can recruit cavalry at a lower level and faster rate, but they still need complete stable building lines to recruit their special cavalry units.
To install, just replace your export_descr_buildings.txt with mine. Leave the original backup as it might not work on yours even if it worked on mine.