The fact that an artist did or did not take part in the song-writing, composition or production of a song doesn't take away from the song. However, I personally respect artists that write AND perform their own music - it lends more credibility to their creative process and artistic integrity as a whole. Some major pop stars in the industry will co-write from time to time, but overall, most don't.
That's why I'm pretty obsessed with singers like Tinashe who basically built herself up through releasing mixtapes online before signing a contract.. She writes, she produces, she composes, she sings, she dances, she does it all. Her voice and music style might not be for everyone, but at least she's a genuine artist ♡