There has to be a good reason why he hasnt trained up someone to black belt in 12 years, that is quite unnatural. It doesnt sound to me that being a good or bad business manager is the root, it maybe that the students do not stay long enough even though you have been there for four years.
It certainly wont have anything to do with testing your patience.
I wonder if, with all respect to your teacher,whether if in fact he is a good teacher because you are only seeing it from a low kyu perspective and if all he has ever shown you is low level stuff for four years, but happens to be a great guy and gets the message across well, then I am afraid to say there should be more to it than that.
I think I agree with the others that it would be helpful for you to have some separate advanced tuition,at least that way you will see if he has more in the bag than what he has taught you over the past four years.
Hope this helps.
osu
Trevor
Trevor Gilbert
("If I had to select one quality, one personal characteristic that I regard as being most highly correlated with success, whatever the field, I would pick the trait of persistence. Determination. The will to endure to the end, to get knocked down seventy times and get up off the floor saying "Here goes number seventy-one" - Richard M. DeVos)