that is inherantly flawed logic. a great singer shoudl eb able to shine even if she doesnt write her own music.
look at arethra franklin, she writes a little but not all.
and its the opposite as well, a great writer should not have to be a great singer to be heard.
the symbiotic relationship is much needed to bring the best music possible.
some peoepl are just lucky, they can write and sing, but i dont think its needed.