They just choose such way because it was more logic for game creator. For me its not so big lie, for me clan leader is just meaning of some clan independence. If clan is not independent they are not clan leaders.
In game smallest cell is "kori" such county like I say earlier. So for them is kokujin title, and this is OK - such high samurai landlord.
One "kori" for example islands, or more "kori" are forming japanease "kuni" as province and for them are daimyo - and this is also OK for me. Why? Because as clan lader you collect titles from every kuni you control. So in practic you can be daimyo of Owari, Daimyo of Goto, Daimyo of Kii etc. And there was such titulature some close to our European, that people say every of title had they master. Like in Europe was Duke of Silesia, Duke of Pommerania, Duke of Wales etc. And as CLAN LEADER you can grant daimyo title of such kuni to your vassal. And its historical true. He was clan leader? He was. Every of kuni represent daimyo title? They do. So its for me all OK.
Fudai title is later invention of Tokugawa shoguns from what I read. And "Karo" was just advisors, in game you had them just as "advisors" choosen from court. And generals, army leaders are choosen from your advisors. Shame that you cant have only normal generals. Like 12 generals of Oda.
Only in Shogun Total War, clan leaders was equal to daimyo title. But in reality they was not for example "Daimyo of Hojo clan" Only they was daimyo of provinces they own. In Total War series there is no feudal ledder.
Its only my opinion, and Im not lawyer of Paradox. But for me this system have good logic. Maybe because my history knowledge of Japan is less than European.
