I remember back to some time ago when we were argueing if China would induct Su-35. No body agreed that except one banned idiot. Since China bought the Su-35 out of our surprise, it won't be surprise anymore if China eventually add Su-57 to its fleet.
Even the US would buy the Su-57 if it was offered. That explains everything that needs explaining on the Su-35 and Su-57 purchase topic.
For China, they'd still buy su-57 even if PLAAF is testing 6th gen fighters, assuming the price is right.
The US would love to buy some Su-35s today if the Russians would sell to them. This doesn't mean the Su-35 is superior to the F-22 and F-35 like Indian logic would suggest.