I never said the Su-35 was "too advanced". All I'm saying is that the Su-35 was purchased to have immediate combat power. The J-11D, which is on the same level as the Su-35, has been delayed either due to testing or shifting priorities. China is ahead of Russian in several of the areas you just mentioned ... but China is behind in fielding TVC, which is a feature of the Su-35. Hence, the purchase of the Su-35 ...
Why does it make no sense? Let me remind you that Russia was insistent on at least 48 aircraft for the better half of a decade ... but due to crippling sanctions in 2014, they relented to 24 (which made the offer more attractive). And the "commonest inference" is simply wrong; China cannot make up for engine maturity by buying the Su-35. How is the purchase supposed to alleviate this problem in any way, shape, or form? Also, the Taihang engine series has matured considerably over the past two years ... we're seeing them on the J-20, J-10 TVC, and Y-20 ... which makes it less likely for a Su-35 purchase out of engine purposes. I have already given you several answers ... I'm not sure why you find it so difficult to contemplate.