It could be an advantage for the US, but it looks to me like a liability for Russia, since they don't have enough manpower to guard it.
In case of war between China and Russia I could easily see Chinese invading large swaths of lands without any meaningful opposition. Populations in eastern Russia are treated more like than colonial subjects than regular citizen, so I don't think they will mind too much a new overlord.
Assuming they had the troops to get there, they cannot move all of them to the border with China and leave the western front unguarded
In case of war between China and Russia I could easily see Chinese invading large swaths of lands without any meaningful opposition. Populations in eastern Russia are treated more like than colonial subjects than regular citizen, so I don't think they will mind too much a new overlord.
Assuming they had the troops to get there, they cannot move all of them to the border with China and leave the western front unguarded