In another section of the site I explained how record production is a team
effort, with the record producer in the role of team leader, with the record
company's A&R manager having the absolute final say.
In some types of production, the rest of the team consists of the band, and
no-one else need be involved.
But for a solo artist, there has to be a musical backing of some sort, and
unless he or she happens to be an extremely talented multi-instrumentalist (or
the producer is), then extra musical input will be necessary, from the arranger,
programmer and session musicians.