Still, I'd like to argue that their value-add is much lower today, since they both distribution and marketing/outreach can be handled by the artist herself (more or less).

I remember an interview with Christina Aquilera about doing her first music video. The studio had people on set with reports on exactly what highschool girls in the target market were wearing, how they did their make-up. She was meant to look like the pretty girl at school, every school, not a model or red-carpet celeb with professionals doing their hair. That video was the result of hundreds of hours of market research. She was under no illusions about who defined her image. Net result: massive sales and filled stadiums.