well if anything he's the one coordinating the repetitions and stuff, it's a collective effort and he's the one making it happens. He's giving the beat so everybody plays at the same time and he's the one making sure everybody plays as loud or quiet as they should.
Similarly to in a rock band, individual virtuosity would mean nothing without the sound engineer / producer making sure you hear music, not noise.
Also the composer is the one that actually wrote the music, he's literally the author of the score.