China has faced less strict sanctions and has been able to engage in much more aggressive academic and industrial espionage than post-Soviet Russia. It remains to be seen whether, now that sanctions have ramped up, and access to Western/Japanese research and expertise is being curtailed, they can maintain what they've already replicated, never mind build on it to make newer and better things.
China simply outspends russia a hundred times over. When you account for china's full security budget it's almost the same as US defense spending when accounting for PPP.
China is also the world's factory and many components of modern weapons are dual use goods of which China is the supply chain. The problem that no one dares speak is that there is no wholly domestic supply chain for most electronics and other components anymore. If war were to break out with China US defense production would halt immediately.
