I don't think the requirement is strictly necessary because in practice it was regularly the other way around: successful exam takers were relegated to regional governorship while the central government was filled with favorites and cronies. There is however no mechanic preventing chars with low learning from being rulers. At best, employing people with low learning should only invoke some mallus, although since there is no confucian religion it's hard to say who this would apply to. In terms of realism, it's probably more important is to prevent local governors to also serve as councilors, but this obviously prevents players from playing as councilors.Confucian Bureaucracy and Chinese Imperial currently (6.0.0) require all council members (and the Designated Regent) to have 10 Learning, regardless of the position they hold, to simulate the appointees passing some form of examination. The Learning requirement will be changed to 12/10/8/6 for emperor/king/duke/count rulers in 6.0.1, as the current value is a bit too restrictive for lower title rulers.