Now, there are a couple of other things that would help. First, you should consider changing the religions of China and Japan. I suggest catholic for Japan and orthodox or sunni for China. Then they will be able to deal more with the other dudes, plus they will get colonists for some expansion. Imagine Japan expanding into Southeast Asia many centuries early, or China burrowing its way through that Eurasian pipeline, to kick Russia right in the donkey. Finally, to get any real fun in the first few hundred hours of the game, have some European seas or provinces explored by China/Japan, or even better, give them historical(?) explorers!