I think the situation is culturally very different in the UK. But my experience of supervision is very collaborative and not authoritative. ie the supervisor is not instructing or sticking their oar in when it comes to what they don't understand.
It's a place where the therapist can freely explore their own unconscious motivations and responses to working with their clients and the supervisor is very respectful of the fact that they are not the one in the room, and don't presume to know. A lot like how the therapist can't presume to know what's best for their clients.
In my experience there is a good degree of scrutiny of supervisory practice. In my case, my supervisor has a supervisor (my supervisor also has 40 years experience). It's just a massive cultural difference I think. But I'm glad I have a therapist who values his supervision. It's made a huge difference when we've had ruptures and he has had that space to reflect and explore what has been happening at his end.