So this was the new equipment Yankeesama was talking about… Sheesh. China definitely demonstrated tremendous good will. Russia should at least have sent Su-35s.
You mean Su-57? China has Su-35 to fly with and against for playtime fun.
Russia is by many accounts willing to sell Su-57 as an export variant. Allegedly Algeria has already placed an order. I would imagine Russia would have no qualms showing off the Su-57 in relative secrecy to China, not during a high profile exercise where it would create a bigger fuss in the defence world. If China asks for a more detailed viewing and to fly against it, I would imagine such a thing could be organised. I doubt it happens though since Russia truly isn't building Su-57 at a rate they should be currently satisfied with. No matter what one might choose to believe, Russia wants more Su-57s if it is a good fighter. It's as simple as that. There is no good reason why they'd not be building them at a faster pace unless they have something better or the benefits of the Su-57 are marginal compared to modernised Flankers because they have absolutely no fear of American stealth fighters at all for whatever reason that might be.
Personally I think it's just the usual LRIP and relatively more sensible budgeting where Russian MIC after the Soviet Union's dissolution has slowed considerably and delivered new weapons with some delay. Russia's security is underpinned by its massive nuclear forces and despite getting involved into regional and proxy wars even directly against the US, the US has not really engaged Russia conventionally at all. That is what a reasonably good conventional military gets you when it is backed by the world's equal first nuclear stockpile and delivery systems.
If you listen to the talk, at least one of the characters have better insider knowledge than us here, they know the Russians well and may have close colleagues work alongside them in exercises or hear first hand accounts. The stuff mentioned isn't surprising but it also explains or rather hints at why China sort of allowed the use of more modern weapons in this exercise compared to what Russia keeps bringing to exercises. It's worth listening to until around the 30min to 45min mark.