OR: Long story short, China's very greatness and stability condemns it to few leaderheads.
Actually, stability is not the factor ascribed for the number of leaderheads. I guest your theory is that CIV4 should put the num of leaders in accordance to number of nations in an area; The Europe has many inunified nation thus it can has as many leaderheads as the number of nations permitted.
But IMO, the num of leaders does not affect the game stability, having above 10 leaders for china(And I think they should) won't let china be the most cheating civilization in CIV4, you still could only choose 1 leader for each game.
Besides, China has not been always stable, throughout the history China had been broken into several countries during many civil wars. And during those periods many great leaders appeared seeking to unify China. Thus saying in Chinese idiom " Great People emerged in a Time Of Chaos".
If some of the now-non-existed European Nations such as Holy Roman Empire , Byzantine, Greek, Rome, can be accepted as the playable civilization in CIV4. Then, why don't we put the preunified Zhou Dynasty, Shang Dynasty, the 7 Greater nations during the Warring State Periods as the playable civilization in CIV5. The culture i.e. writing system in those periods also largely different from the post-Unified China.
If some barbaric war-mongering tribes such as Celt ( sorry I don't mean the same to the now Scottish and Welsh) who fought naked can still be accepted as "civilization", then We may also accept Malays Kingdom in CIV5. if some failed general such as Hannibal could be esteemed as leader, then, a lot of Chinese Generals (Yue Fei, Zu Ge Liang, Zheng Cheng Gong....) as long as Japanese Warlord(Nobunaga) could also be accepted as playable leaders(with ten folds of qualification).
I don't mean that Europe does not qualified to have many leaders, actually I admire the Europeans of their creativity and their contributions to the modern Civilization, technologies, philosophies, Science and Democracy (in the light of CHRISTIANITY) in the latter age. But just mumbling about the leaderheads of China.
By the way, I would totally satisfied if They just replaced the leaderhead of Mao Ze Dong with Dr Sun Yat-Sen, who was the founding father of democracy and modernity in China.
