My T does not have a supervisor. She's been in practice for 20+ years. She does have a peer group that she consults with weekly.

For me, it was not a concern. My T has her life together and she's phenomenal to work with. If she has a client that she needs feedback on, she takes that to her peer group or may consult with a p-doc or other resources.

I wouldn't consider it a deal breaker unless the T was very new to the profession.