Mongol army needs more unit variety.

[Knight Templar]

AFAIK, Mongol army who invaded Europe were only cavalry, so it would be nice Golden Horden has bigger variety of cavalry troops. They have only MHC and MHA, and Steppe cavalry which can be trained in steppe provinces.
I agree Golden Horde invades with too little (twice as more should be good) troops, I've never seen them (in game) holding Hungary and Silesia (like they historically did). Their units should also tire slower on the battlefield, and, like matteus said, their generals should have more command stars.

[matteus the inbred]

Ironically, I bothered to go and check some sources. As you say, KT, the initial invasion was entirely cavalry stuff, but later incarnations of the Golden Horde (from about 1251) actually used foot archers called Bessermeni (local Muslim town militias) and had Armenian archers, Siberian tribesmen, and even Italian mercenary crossbowmen called 'Fryazei' in their armies.
I suppose therefore that the most accurate compromise would be an initial Horde invasion of entirely cavalry (and siege weapons, I guess), then later they get reinforcements of mixed cavalry and foot...