Five years ago the Russians wouldn't sell their most advanced fighters to China. So it's pretty irrlevant unless they're willing to sell what China needs. So it's safe to say if the Su-35 is far superior to anything China has, it wouldn't be sold. Since they're trying to sell it to China, it must not be at most that much better than what China is capable domestically.
Er... don't really understand that.
ten years ago, five years ago or even now, Russia or any countries in the world will not sell their most advance fighters or system to any country, until they have something better in their arsenal. So how come it is safe to say that if the Su-35 is far superior to anything China has, it wouldn't be sold? Why would the Russian try to sell something that is inferior to what China or any country already has? Wouldn't it be for nought (remember, even marketing of a product cost money).
If it was said that if the Su-35 represent the highest technology that the Russian had, then it would be safe to say that that aircraft will not be offered to any international customers, at least the same one that will be flown in Russia (downgraded version might still be offered).