Could you specify what you mean? China was completely conquered by the Mongols and subsumed under an ethnic Mongol dynasty for about a century. I hardly think that counts as "tanking damage."

Jin China was progressively destroyed by the Mongols - perhaps "tanking damage" isn't accurate. The destruction of Jin China took 23 years, but for much of that time, the main Mongol army was elsewhere. The Mongol-Jin war can be divided into 3 main phases:

1. From the start of the war (1211) to the conquest of Beijing (1216). The Mongol forces might have been about 70,000. The Jin field armies that opposed them were smaller (perhaps about 40,000), and had a smaller proportion of cavalry, but these could be supported by militia and local garrisons. The Jin, with a population of about 55 million, had a large pool on military manpower - regional warlords could raise armies of 30,000. Thus, the defeat, or even the total destruction of a Jin field army would not leave the Jin Empire defenseless. Coupled with the initially poor ability of the Mongols to take strongly fortified cities, it took the Mongols until 1216 until they captured Beijing.

2. Indecisive fighting while the main Mongol army was elsewhere. Mongol armies were smaller (c. 30,000) and Jin armies were larger (up to 100,000?). Mongol operations often consisted of invading Jin territory in autumn, gaining control of the invaded regions, and then withdrawing to the north for summer, whereupon the Jin would re-establish control.

3. The destruction of the Jin, 1230-1234. Following the destruction of Xi Xia (1225-1227), the main Mongol army returned to China, and the war against the Jin became the main effort for the Mongols in 1230. Jin armies were larger than before (at times, 100,000 or larger) and better, but they were facing a much stronger Mongol effort.

Result: complete destruction of the Jin Empire (population 55 million) in 9 years of main-effort warfare (phases 1 and 3).

What happened when the Mongols went west?

1. Destruction of the Kwarezmian Empire (population 5 million) in 3 years (1218-1221). While the main fighting was over by late 1221, mopping-up operations continued until 1224. Mongol army perhaps 100,000 to 150,000 strong, while the Khwarezmian field army was about 40,000 (supporting by static garrisons).

2. Conquest of Mesopotamia in 2 years (1256-1258). Mongol army perhaps 100,000 to 150,000 strong, while the Abbasid army defending Baghdad was 50,000 at most.

3. Defeat by Egypt (population c. 8 million).

Comparing the conquest of Jin China with the conquest of Khwarezmia and Mesopotamia: approximately 20% of the population was conquered in about 50% of the time (not counting operations in Khwarezmia after 1221).

For further comparison: the destruction of Xi Xia (population 3 million) in 2 years (1225-1227).

Next, we can consider the ability of Song China (population c. 70 million) to "tank damage". Once the frontier defences were broken through (the capture of Xiangyang, 1273, at the end of a 5 year siege), the Song Empire was destroyed in 5 years (1279). The Mongol armies in this invasion were larger than earlier, but the Song Empire also had large armies, much larger than the armies faced by the Mongols in the west. For this campaign (but not for Khwarezmia or Mesopotamia compared to the conquest of the Jin) that "the Mongols get fed by previous conquests", but it was not a walkover. Before the main attack on the Song, the Mongols and the Song fought for the control of Sichuan, for about 30 years.

(Estimates of army sizes mostly from C. F. Sverdrup, The Mongol Conquests, Helion 2017.)