I recall reading somewhere back in one of these other threads that the Mongols were taking too long to conquer China.
The China (Jin/Song/Xi Xia) theater was the Mongols' most difficult campaign to wage by far, compared to everything else.
It took two generations to do it and was by no means, quick.
The way I see it (for the AI), the Mongol invasions should stimulate/accelerate Chinese collapse,
then pick off parts/all of it as it falls into a collection of Independents.
That way, it helps India too (or at least human India), so that it may be a little bit easier to achieve the third UHV goal with China out of the picture.
I pointed out the slow Mongolian conquest of China earlier but to no avail. Currently there are three problems with China:
1) The Tech rate is extremely fast; I knew from the start that this was a bad idea; what was wrong with how things were before?
2) The Mongolian conquest of China is extremely slow.
3) China does not respawn after the Mongolian conquests which leads to wierd looking map with Khmer controlling southern China, Korea northern and Japanese controlling some cities on the coast.