You're missing the point of the analogy.
You said: "Manchus are Chinese. Manchu's soil, of course equal to Chinese soil."
Why can't I say: "Mongols are Chinese. Mongol's soil, of course equal to Chinese soil."
Do you get the logic?
If you can say that all Manchu territory before their formal transformation into a "Chinese" entity is Chinese territory, then one could say that for all of the ethnic minorities in China.
The list could go on and on.
I could very well say: "Russians are Chinese. Russian's soil, of course equal to Chinese soil."
This presents quite an enigma. Russians and Mongols are both official ethnic minorities of China. They are therefore Chinese.
Is it logical to take that one step further and to claim that the histories of these ethnic groups, before becoming Chinese (In the case of Russians never) as a part of Chinese history?
If so, we have a few interesting historical instances.
The Russians were conquered by the Mongols, but later were able to kick the Mongols out of their land, thus gaining independence.
But since Russians and Mongols are both Chinese...The Chinese were conquered by the Chinese, but later on the Chinese kicked the Chinese out of their land, thus gaining independence.
Am I making sense?
Sorry, I made a mistake to say Manchus are Chinese so Manchus soil are Chinese soil. Below is my correction:
The Manchus recieved the mandate of heaven to rule China, so any Manchu's territories are Chinese territories. As for the entire Mongol Empire, only the Emperor of Yuan Dynasty had the mandate of heaven, so Chinese territories are limited to Yuan Dynasty.