No big (visible) structural modifications means that the original design is fine as expected ( recently it's said that the PAK FA has some structural problems - by Sukhoi CEO himself?), thus good news IMO.
It that reasonable to assume that J-20's avionics are a league ahead of the best of Rafale?
Speeder did you have a link to the Pak Fa probs, seemed from what I did find, it was rear center fuse, and vert stabs?