No, it's not true, there are no prominent conductors that cannot play an instrument (or sing at a high level). A conductor should have a deep understanding of

No, it's not true, there are no prominent conductors that cannot play an instrument (or sing at a high level). A conductor should have a deep understanding of music, theory, and rehearsal pedagogy. At least in current western schools of music I don't see how you would explore these topics outside of the study of an instrument. Maybe there is some esoteric path to this; I just can't imagine how you go to Berklee and begin to explore the nuances of a composition without ever engaging with it as an instrumentalist. On top of that, the conductor isn't just engaged at performances, they're also responsible for leading rehearsals. If they've never deliberate practiced the learning of music from an instrumentalist perspective I think they would be very hard-pressed to structure strategies for getting the larger group to a high level.