Contemporary Chinese writers ascribed Jurchen success over the Liao and Northern Song mainly to their use of cavalry units. They adopted cavalry tactics that were very close to their traditional hunting tactics. Although I also read that they sometimes chaiend their horses together as a certain/if not special battle tactic. Personally I fail to see how that worked but oh well.
Anyhow, after the founding of the Jin Dynasty, the Jin absorbed a lot of the Chinese soldiers who were fighting against the, they adopted chinese weaponry and warfare tactics. (their cavalry was always a prime unit though among their ranks)
The Jin are consisted mainly of the chinese because it would be more the 'Liao absorbed' soldiers that would have gone into Mongolia at the time as war parties. Since the Jin activity in Mongolia didn't entirely happen historically, I was waiting for Great Kahn, my project that is a direct conflict between mongol and the Chinese to (fix) any gaps in historical accuracy.
The way I see it, the Chin would have had superior numbers and armours, but they'd have left the majority of the cavalry in Jin, not floating around Mongolia pwning everyone. It also helped add a variety to the fighting style, there's only so much i could take off (HORSE ON HORSE ACTION)
I need foot soldiers and this was the ideal solution for it.
The Great kahn will foxu more on the Jin, there will be HUGE varied armies consisting of Jin and Song soldiers, new armorus that wil ltry and reflect the actual armour used by the Jin and the Song and various other things. At the moment we are concentrating on the 'mongolian war' front. Where Genghis unifies the various tribes.