You seem to hold two ideas in your head that are fighting for the share of the brain time: that conceptual albums are better than semi-random collections of tracks, and that artists writing their own songs are better than those getting songs written for them. Somehow you can't distinguish the two, or at least write as if you do.

Meanwhile, e.g. Nico's ‘Chelsea Girl’ has only one song co-written by Nico, but is a great album with two songs that are regularly featured in media decades later: ‘These Days’ and ‘The Fairest of the Seasons’, and also the splendid ‘Wrap Your Troubles In Dreams’.

Also btw, you might be surprised at how many popular songs are covers. This was particularly widespread in the sixties, when the same song could've been sold to several different performers in a few weeks.

After all, songwriting and singing or playing music are skills that aren't inherently related. Have you heard many poets sing their poems in a town square while playing a guitar or some shit like that? Many popular bands have someone like the drummer be the primary songwriter. Even the lyrics and the music are often written by two different people. Plenty of great labels have producers, songwriters, and house bands that are separate from singing artists that they publish — this was prevalent in the seventies with labels such as Stax (with Booker T. and the M.G.'s as the house producer and the band). It's changed somewhat in the recent times, with labels playing a smaller role both with the ascent of streaming and the preference for singer-songwriters.

Lastly, recall that e.g. Mozart was a great composer, but could perform perhaps just a few of his own pieces, as he was neither an orchestra, nor a conductor or an operatic singer, for whom he wrote.