You might want to remember when you are trashing some singer for their performance in some opera or other that the quality of the music you are hearing is the responsibility of the conductor. It means nothing that the orchestra sounds great if the singers are boring and unmusical and uncoordinated with the players. He's responsible for all of it, not just the orchestra. It's all one piece of music that everyone is making together. It must be conceived as a single piece and brought to reality by the conductor.