First of all, Ronin is a skirmish game so compositions are merely an extrapolation.
Secondly, how could you claim that?
Mongol armies have been described in contempory works of Europeans, Russians, Byzantines, Turks, Mamluks, Arabs, Persians, China, India, Japan ,etc. The abundance of contemporary artwork also illustrates compositions of Mongol forces in the field.
Quite detailed records exist in Chinese of the Yuan (Mongol) Dynasty, including compositions of both armies that invaded Japan. (This is source of infantry components of Mongol armies not seen in West.) Later Qing Dynasty records the details of Mongol Banners who fought for the Jurchen/Qing from the 1600s up to 1911.
I was already an avid wargamer while an undergrad at UC Berkeley, one of my favorite classes was the semester I spent studying the Nomads of Eastern Asia where my professor shared his research in the steppe people and how they contributed troop types based on individual wealth. The wealth (based on horse & cattle) dictated what one had to bring on campaign. This showed that Mongol Tumens were composed of around 30-40% armored lancers with the remaining being bowmen wearing either felt/fabric coats or some form of leather/padded leather.
On campaign in the West, records show Mongols fighting in 5 ranks, the first 3 were horse archers and the last 2 were composed of lancers wearing differing levels of armor.
Over time, as the Mongols fractured into their separate Khanates, they tended to adopt organizations of their conquered lands/peoples/climates, also recorded for history.
