Are Dolly Parton and Tracy Chapman better artists than Whitney Houston and Celine Dion as they write their own?

I'm doing an essay on this, and would like your opinions. I am stating that Dolly Parton and Tracy Chapman are better artists than Whitney Houston and Celine Dion because they write their own songs and play instruments. They create and perform art. Celine and Whitney just sing what other people have written, and don't create art themselves. Neither plays any instruments either.