Not everyone is a songwriter, just like everyone is not a singer, instrumentalist, sportsman/woman or rocket scientist.
Let’s take a look at the fifties & sixties, a time of many great songs and artists. Many great artists never composed their own songs but could sell a good song. Elvis Presley, Tom Jones, Cilla Black, Tina Turner, The Supremes, Aretha Franklin, the list goes on. There are equally a list of great songwriters, Bacharach/David, Paul Anka, Boyce/Hart, Phil Spector.
This also applies to instrumentalists as well. Don’t play an average song when you can play a good/great song. Just because you wrote it doesn’t make it any good.
What I’m seeing today is a lack of great new songs and there are way too many singer/songwriters out there. Just what the world needs, another singer/songwriter, right? If you’re a great singer then find a great songwriter to work with, likewise if you’re a great songwriter find a great singer to work with. If you’re great at both, then fantastic.