In official Russian news sources, the Su-57D is defined as "a combat trainer and a command and control aircraft."
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Note the choice of words here: the function of the aircraft as a trainer is placed first. This profoundly explains why the rear-seat occupants' seating position is so high. This is also the core reason for the fundamental difference in design philosophy between it and the J-20S. From inception to completion, the J-20S was never considered for use as a trainer aircraft.
Buried within the official news release is a hidden detail:
This aircraft was developed by the manufacturer on its own initiative.
The subtext of this statement is as follows:
The Russian military was not involved in the Su-57D project. Consequently, there remains significant uncertainty regarding whether the Russian military will ultimately procure the Su-57D in the future. (This situation mirrors the early stages of the FC-31/J-35 project.)
Furthermore, the official news release implicitly suggests that the Su-57D is intended for the overseas export market. However, whether it has been specifically tailored for India remains a matter of considerable doubt.