I think it depends on the level of your talent in terms of composing. If you are an excellent vocalist and an excellent song writer, then you'd be more talented then someone who is just an excellent vocalist. But if you are an average singer and an average song writer, then you wouldn't be as talented as someone who is just an excellent vocalist, etc... People like Mariah and Madonna I always assumed mainly wrote the lyrics and maybe had some minimal input on the composition of the music, ala Justin Timberlake, but never actually composed an entire song on their own. I never saw either of those two having that ability or talent. Of course, comparing the two is a good example of my first point of how you would rank talent. I would say Mariah is more talented then Madonna simply because, while both are singers and have some input on their song writing, Mariah is an excellent vocalist and an average song writer, while Madonna I would say is an average to below average vocalist and an average song writer.