China and Russia have been classically opposed and clashing forces since the 1800s, even under dual-communist regimes. It was so bad in the 1960s that the Soviets wanted to engage in pre-emptive nuclear war with China.

https://en.wikipedia.org/wiki/Sino-Soviet_split

Making Russia completely dependent on China economically will put a leash on Russia, effectively establishing it as a Chinese protectorate much like the Li–Lobanov Treaty made China a Russian protectorate.