Well to be honest, I just think the Russians ran out of money as this aircraft project would have never moved along without the Indian $. Judging from the points in this article, they had to cut corners, older engines, half assed "stealth" profile. Not surprising, as Sukhoi has built some fantastic planes, SU-35, SU-37, SU-47, but they only built a few as demonstrators for air shows (eg. annual Paris Airshow), not having the dollars to put them into active service. They built and marketed the SU-30 to a variety of nations (Sukhoi 30 MKI to India as an example)but the Indians reportedly found them to be inferior based on proposed adversaries, and are planning (as reported) to buy some French Rafales as their front line military interceptor.
As thye say, money talks !