I ask about whose class you attended because my own experience there was quite positive, particularly in the classes of Endo and Miyamoto. I saw none of the tension you spoke of, and I was treated quite well, even as a gaijin. There was byplay and banter in the locker room, with Endo taking part. So YMMV.
Nope not Endo or Miyamoto whose classes were highly recommended by my contacts.
I rather not mention any names here for fear of offending anyone