Yes and No. Like most things it comes down to personal preference. I don't think that I've seen hardly anyone who does really well in the middle. Either they use custom brushes and hardly ever paint with just a circular brush or vice versa.
Here's some good examples:
- Lots of custom brushes
- Mathias, Lots of custom brushes
dylancolestudio.com - Lots of use of the circular brush but painting really fine
- Lots of circular brushes
It takes alot of practice and hard work to get custom brushes to work like real ones, I think that's why you'll see alot of conceptual artists use custom brushes because they can be very dynamic and unpredictable and give you alot of happy mistakes. In matte painting it can be really hard to use something so unpredictable to create fine work and so that's why I don't think you'll see very many matte artists use custom brushes (cept for maybe a pallette knife) in the final stages of a painting.