certain folks may only perform a short period while others the whole night. Yes. But there is a shitload of rehearsal that goes into the performance for those few hours or minutes. I have been one of those singers before back in my college/post-college years. The diversity of the instruments and magnitude of the ensemble allows for the beauty of the music to speak. Beethoven knew what the hell he was doing. I suppose the ensemble and the performance parallel much of what goes on in the real world. Yes, but the music is far from inefficient if you are seeking a certain quality. We may be able to reproduce that same sound with electronics, but not the experience of so many voices of instruments live.
We can also record it and play it back over and over, but that doesn't provide the same experience, nor does it encourage expansion of experience. There is a lot of value in inefficiency, which is why so much of the problems we have in the world exist through maximization of wealth, as it is a process of improving economic efficiency, not encouraging human growth.