The Russian-Chinese relationship is best described as an "Axis of Convenience" rather than any genuine alliance of mutual ideological or political system doctrines. The bonding glue is anti-US or anti-West hegemony, mutual respect, and multi-polarity, BUT....after Putin dies and Russia-US relations normalize with Putin's successor and China becomes too strong, just watch. The pendulum can swing in the other direction, Nixon-style to Russia.
I see the counterveiling points below.
The issue is that the European Union and NATO are next to the core heartlands of European Russia where the vast majority of the population and economic activity reside. It's only 500km from Ukraine to Moscow, so there's no strategic depth if a few battles are lost.
At the same time, the EU comprises a much larger economic bloc. If the EU expands to the Russian border, Russia faces the prospect of being a resource appendage and being dependent on EU trade whilst the reverse is not true. That will keep the disputes in Ukraine and the Baltic States alive.
In comparison, China can grow as large as it wants, because the Chinese-Russia border is sparsely populated which limits the amount of economic interaction and dependency, particularly since the majority of the Russian population and industry is in European Russia. From a military perspective, because Russia and China share a land border and both have nukes, there also isn't any ambiguity about the effects of a war between them.