The argument that a composer being some how superior to performers is obviously an ignorant one. Composers are just another part of the process. They create art just as performers do.
Looking at a musical performance as a communion of musical ideas, or rather ideas themselves, which the performers receive from the work before them (no doubt conceived by some person even if the artist remains anonymous); and of course we have to assume that the ideas presented are only an interpretation of the composers original idea, and to a room full of musician this is obvious however, not talking about a motive or some fantastic melody, but the larger idea of the piece: the larger inspiration: the message of the work: the all important question “ what is the music saying or mean?”
I think any composer would tell you that when composing, even if he/she did not start the work with a specific “big idea” in mind, that the work would eventually develop one; furthermore it become extremely clear to the composer and if they are good at what they do it will show clearly in their music. It is in fact the mark of a great composer, one who conveys ideas so clearly in their work that it is obvious to a listening audience. But, back to the subject at hand. Since the composers ideas must be interpreted through an inexact notational system the performers can only do their best to play the work as the composer intended, even with the composer present it is rare that his ideas and the performance will match completely. That is to say “the composer’s work of art is purest in his head”. He must then try to recreate his art on paper, in at way that conveys an accurate message to the performers. A great composer will retain, in an absolute sense, the clarity of his idea when he/she writes it down. In this way music is constantly being created and recreated, by each conductor, performance and by each listener’s interpretation, to name a few of the places in which this happens. In many ways this constant happening gives us, as musicians tremendous opportunity to fail, and in this way a tremendous will to succeed.