...from the perspective of having had a master (yours) and now having dumped him I can see that history  has moved on. There are other options open to the enquirer.

The "master is essential" idea is yesterdays news. Sure there is an esoteric  tradition of masters initiating students, that is as old as the hills, but , based on experience of escaping from a master and the direction of my subsequent transformation, I can say that that the guru/disciple tradition is an antique one, and thoroughly optional. At best a starting point, but more likely destructive to self in the long run.

Spiritual Independence, like power, is never given, it has to be taken.

Your protective attitude to your master is a good example of the kind of self  limitation and waste of energy that devotion imposes on its practitioners.

As for evaluating the mastery of esoteric knowledge, (Capital K Knowledge is a non-word for most purposes of communication imo), it is a possibility and done by empathising with as broad a spectrum people and events as possible.

 In a twenty first century context, I think a master will only make you exclusive and defensive. and probably arrogant.

Love

Bryn