Composing and conducting are two completely different specialties.
I agree. Creation and performance are two distinct talents which don't always co-exist in the same person (though often they do, of course, depending on the discipline - e.g. composer pianists). In a literary context this is illustrated all too often when poets read their own work: most of them do it very badly, I am sorry to say. I have heard far too many dreadful readings on BBC Radio by living poets who either chant their poems in a dreary voice in which every word seems so weighed down with melancholy "import" that all vitality is lost and the listener quickly gets irritated or adopt an equally alienating monotone (T.S. Eliot is an example of the latter) which is very boring, whereas if the poem is given to a trained actor to read it suddenly comes alive and engages the listener.