In Life Patterns, we find that the same pattern has healthy and unhealthy components. We work with the healthy side of the pattern, and, even though a disorder, which is an unordered, non-specific approach to problems exists, it is still a pattern. If it was not a pattern, no one could make it into a diagnosis.
The question is does the diagnosis help in psychotherapy, I don't think so. Knowing the pattern helps. If the client understands both the healthy and unhealthy aspects in the pattern, they can choose which side of the actions and thinking they want to use in life.