Usually when you play the opening as Black you are responding to White's move which takes the initative out of your hands somewhat. There is such a thing as transposing https://en.wikipedia.org/wiki/Transposition_(chess), where you can reach the same position from different sequence of openings. So you can reach positions you are familiar with from a number of different openings.
As far as top players I think you need to be able to have variation in your repertoire if you play the same thing stubbornly you would risk becoming predicable and your opponent can prepare lines against you specifically. It might work for one tournament but afterwards people would have studied the games and developed counters.
As far as top players I think you need to be able to have variation in your repertoire if you play the same thing stubbornly you would risk becoming predicable and your opponent can prepare lines against you specifically. It might work for one tournament but afterwards people would have studied the games and developed counters.