If you play that game, Russia belongs belongs to Sweden, since it wouldn't even exist were it not for the Varangians.
Which is why historical precedence before a certain point is useless.
For example, it's very, very possible that the Egyptian civilization was created by brown people before other races came in. 'Cause then we see that brown people migrated all over the world; Australia, the Americas, the Pacific islands. So would that mean most of the world belongs to Indians?
A lot of Southern Europeans were brown too. As was the Roman civilization. So more credit to Indians.
China can't lay claim over Russian territories simply because they lost it.
CCP's greed? Sure they have greed wrt South China Sea, but you can hardly talk about China's greed when you consider the distance of Manchuria to Beijing and the distance to Moscow. Russia has no business in East Asia at all, it's all an imperial empire without civil liberties. They stole Manchuria from the Chinese in the late 19th century and then pseudo-stole mainland China from the true Chinese rulers in 1949.
It isn't all that simple. They have both been fighting over the region for over 400 years.
Treaty of Nerchinsk - Wikipedia
en.wikipedia.org
Treaty of Aigun - Wikipedia
en.wikipedia.org
Convention of Peking - Wikipedia
en.wikipedia.org
The Chinese regard any treaty that doesn't benefit them as an unequal treaty. So their claims cannot be taken seriously.
India would be about as much use as a chocolate fireguard.
Still much more than Britain.