I would even say that the J-11B is probably more capable than the F-15C from the 1980s due to being newer. And I definitely agree that the J-11BG would have the decisive edge against the F-15C.
For the other fighters you mentioned, other users have stated that J-10C is more or less comparable with the Rafale (especially if even newer versions of the J-10 enter service). The F-16V is somewhat overrated and I have no doubts that the J-10C is at least slightly superior to it overall. Why? The J-10C benefits from reduced RCS, superior kinematic performance (although less relevant in modern aerial combat), superior weapons suite, and has IRST integrated. F-16V is a significant upgrade over older F-16C/D Block 52, but compared to the upgrades on the J-10C, the improvements are relatively limited in comparison. The F-21 is still vaporware and I doubt it would ever be inducted into Indian service. It would be a critical logistical error to induct yet another plane that their pilots have no experience with in large numbers. The relatively limited number of Rafales is probably enough of a headache, but at least they have prior experience with French Mirages. And as far as I know, the F-15EX is basically the American counterpart to the J-16.
All of the advantages of the J-11D that you mentioned here are already present in the form of the J-16, which has reduced RCS, better avionics, far better payload, and superior engines. The only difference is that it is a tandem-seated rather than a single-seater, but that does not imply a disadvantage (except maybe slightly reduced kinematic performance and slightly shorter range). J-16 can easily perform air superiority missions equally as good as the J-11D, and there is no indication that having another pilot would somehow reduce that capability. On the other hand, by having another pilot, the J-16 can also ground strike missions better than the J-11D. And it is already established that the J-16 is the ordinance carrier for the J-20 and AWACS. So really, it is actually the J-16 that negates the benefits of inducting the J-11D. The J-11BG is just a midlife upgrade for the J-11B that would further reduce the need for J-11D (in case the J-11D was somehow more cost-efficient than the J-16), because the set of upgrades of the J-11BG would probably be comprised of most of the improvements of the J-11D, barring reduced RCS (which might be partially negated by the RAM coating that is almost certain to be on the BG version).