His recent videos on stealth are also rather good... compared to the absolute garbage out there (usually Indian) youtube videos on "military matters" with hilariously stupid photoshopped images of a collection of something spamming the thumbnail.
The Su-57 does seem to be the most super maneuverable fighter out there. It's agility is also top notch. I do think it would be nice if China could purchase a non-export variant if it were to buy in volume and then have cooperative efforts to allow the full fledged Su-57 to be integrated with Chinese weapons and make UI more Chinese pilot friendly. India will probably end up buying it off the shelf. I doubt Russia will bother developing a twin seater because there's little point to involve a second pilot with better fusion and optimising through "AI". It's not an attack plane.
If Russia would eventually sell Su-57 with izd.30 and allow Chinese engineers to integrate weapons and some subsystems, it would provide PLAAF with an incredibly capable 5th gen that differs somewhat in role to the J-20 - focuses performance on supersonic regime and seems to focus more on stealth like the two lockmart fighters. Certainly when it comes to pure performance the Su-57 with new engines would fly circles around anything including an F-22 and J-20 with WS-15. Basically an F-22 with two F135s instead but probably better lift and surely much better aerodynamics. Russian production units have improved surface finishing and since the shaping is fine, the rest of the stealth matter is really just covering joints. I suspect they have long solved the fan problem otherwise they wouldn't put it into production. Hopefully by then, the F-22 and F-35 stealth advantages that remain would have eroded so far, they are able to be engaged at BVR distances by just 4th gens with AESAs and modern missiles. There might be something very worthwhile in building the best 5th gen dogfighter. Lots of payload, lots of energy, best performance to carry that payload. We'll see current four 5th gens loading their wings to the brim one day.