A teacher who truly understands the significance of and difference between B# and C is not necessarily a better teacher than any other given teacher. There are obviously many factors. However, in my opinion, the same teacher with the knowledge is better than the version of him/herself without the knowledge. For Josepp, not knowing it is a deal-breaker. For many here, given the specific instrument, genre, and goals, it is not.

In Western music, the B#/C distinction is not trivial or esoteric. It may not be necessary knowledge for many or most performers in a particular genre, but that does not take away from its importance. It's significance goes beyond writing/reading or labeling. It relates to a feature of many types of Western music (and beyond) that plays a role even if the performers are not consciously aware of it. They do not have to be consciously aware of it to perform. Most intuit it and learn through enculturation.

"Folk" musicians and people who don't read music notation have as much music "theory" as anyone else. It's ingenuous to pretend one is being more natural or practical because they aren't well versed in common practice Western music theory. Music is not just sound. It is sound organized by humans, and that organization occurs, to one degree or another, according to certain "rules." Performers in a given musical system subscribe to those rules. Theory describes or, in some cases, prescribes those rules. The B#/C distinction is one result of an attempt to describe the rules.

Josepp may come off as abrasive and rigid in his opinions, but to argue back by discounting the significance of the B#/C distinction is, in my opinion, misguided. Musical truth and understanding shouldn't suffer because one doesn't agree with Josepp's assessment of this one particular situation.