China is either at the leading edge or leading in commercial nuclear tech now. However, it's level is not overwhelming. I think this is largely political, but also partly technical. Russia's VVER reactors are known to have passive safety mechanisms built-in that other 3rd gen reactors don't. I believe the thinking is that China can learn from this design and perhaps incorporate it in future upgrades of Hualong One. Imo, it would have been a better move to cooperate on the BN-800 4th generation reactor technology and I am sure China brought it up, but that is a potential future crown jewel for Russia.
China has a pretty advanced nuclear industry. But the world leader in the nuclear industry is still Russia. Like you said, the latest VVER reactors have safety mechanisms not found in most other reactors in the world like core catchers. China's need for nuclear power is so large, it still cannot meet all its demands by itself either. Russia manages to build nuclear reactors with predictable costs and has built a lot of reactors worldwide over the past decade. They have already built several reactors of this latest VVER design like Leningrad II - 1 and Astravets - 1. So this technology is pretty well proven. This makes them a viable partner in the sector. The joint work on the fast reactors probably helped speed up the Chinese design which could be a future way of generating plutonium for the Chinese MIC. In the long run most of the reactors built in China will be of Chinese make and design but right now it still makes sense to cut deals with the Russians.
Other projects the Russians have which might be of interest in this sector would be the lead-cooled fast reactors (BREST-300), the compact naval reactors (RITM-200), or the space based reactors like those in the Nuklon project.