I do not understand such a craze for Kubilai Khan. Certainly it is an ideal and logical leader for China and Mongolia. Only, I oppose two arguments:
First, he is a close successor of Genghis Khan who is already in the game, (Genghis dies in 1227, Kublai takes power in 1271) and as the developers seek to diversify the eras take two leaders as close chronologically to lead the same country seems to me hardly conceivable.
Secondly, I don't see what Kubilai Khan can bring to the Mongolian civilization present in the game. Mongolia is a warrior civilization, mainly centered on horses. Give it a cultural boost (legitimate in Kublai moreover, especially with the welcome of Marco Polo, the development of Chinese arts etc) would therefore make no sense. However, on the military level, Kublai continued the policy of expansion of Genghis, which does not give it a particular originality on this point. Here I think that the leader system must also provide an alternative way of achieving the ends of the civilization. If the criteria of the leader are too close to the old, or does not make sense with the civilization, I do not see the point.