The reservation is fine in this case.
The only real relaxation is the age limit, which is 28 for General, 31 for OBC and 33 for SC/ST. And in the personal interview round where they have to score 60% versus 70% for General. In terms of actual knowledge, it's the same for all categories. Everything else is the same, like 60% in your degree and your GATE score.
In R&D, you need the best minds. When the country pumps in money to get results you need the best talent. Not someone who got in because he/she was from a particular caste. Reservation in non-R&D based jobs helps the country overall. Best minds promoted. Are you aware of reservation based promotions in DRDO?