For fun, listen to David Cassidy's work during the Partridge Family years, when the studio wrote the songs and provided musicians for him, and compare to Cassidy's post-PF work. What, you never heard of his post-PF work? :-) It's because it's awful.
Ditto the Monkees. At least Cassidy could sing (and damn, he was good). The Monkees couldn't write, sing, or play without massive help.