I never said anything about removing training... it's part of the game.
But you can't train your recruits into battarian archers or vladian squire, They already have to be hired as is. Just like it was in real life. but the other trees allow you to train into cav or archers, which makes it confusion to why they have special rules. specially since the AI spawns with them like they were handing them out on the corner of the main street of a village. I don't know if you have noticed, you can already recruit trained infantry or archer in other factions that have recruit tree that allow you to train them to that unit.
splitting every factions tree into archer/infantry/cav would make way more sense and be less complicated to track.
In real life when they mustered and army, people who had experience with bows would immediately become archers, those with horse would be part of the cavalry and the rest would be in infantry. I'm suggesting a system that would take inspiration of that while also using the system that is already in place. You would still have to upgrade your squire into a knight and your archer into a veteran archer, or maybe split him into a crowsbowmen or mounted archer