The idiocracy attacks together in band as always is when someone points that this system makes no sense. [...] The worse part is the lack of arguments and personal attacks. Way to go.
Now excuse me, I need to go to creative assembly forums say that they have been doing it all wrong all along and when rome conquers Celt territory they should recruit from the celt rooster, not from the roman one. Oh, and I must correct all the history books and say that when crusader armies replenished its troops in Antioch all they got access to was the Turk rooster.
If most people that replied misunderstood you, maybe there is something to think about.
So if I understand now, your complain is not that people can recruit wherever they rule but that recruits are not raised in the culture of the kingdom. Reading your first post, I thought you were advocating the first option.
So, yeah, that could make sense. True, Roman would make recruits legionaries.
But I think we can find other examples that differ. Just watch Ogniem i mieczem/Potop/etc, the movies that are the basis of M&B With Fire And Sword (set in time maybe a bit later, modern era and not medieval per se; but when M&B is exactly set?), you'll see that in Poland-Lithuania, they relied on troops of various background, like Zaporozhian Cossacks.
I think also that viking worked from time to time for some various kingdoms.
So maybe in specific culture like roman-empires inspired, maybe troops should be raised in the kingdom culture. But this restriction can make the game even harder to balance. And maybe not increasing much fun.
What I can agree on is that surely have troops of mixed background should cause leadership difficulties that can be reflected in game (wasn't it in warband? or I dreamt it). Impossible, though, no.
But probably there should be incentives so most lords at least have 75 % of troops matching the kingdom. It is quite obvious that if your troops are composed in majority of khuzait, for instance, what could happen when you are at war against this kingdom? Wouldn't be a risk, in reality, of massive defections?