Hard questions/hard answers
Mr. Porsselius,
This also has been a question that I have struggled with for quite a few years. The answer came when I found that I was able to competently answer the questions of juniors or friends from other arts. Not that my answers were absolutely correct, but more often then not what I said had weight and they were able to take what I said and work it into what they needed. I came to the conclusion that this is what an instructor needs to be able to do. Give the student information that works for them AND leads them to push themselves further.
In terms of generalities, 10 years of solid work should be able to produce a competent teacher in Karate. Not that you are the indisputable authority or anything at that time, but your basics should be polished AND understood so that you can then give them to others. A teacher is a giver of gifts.
I make sure, before I take on a new batch of students that I spend some serious time on the most fundamental elements of my movement. I am getting ready to open new classes in my new hometown, and I am spending a lot of time on the basics, because that is what I will be showing. As long as I really lay a proper foundation, everything else will follow out of that.
Also, at 10 years/ 3rd. dan, etc. a student needs to have new people with which to experiment. That is why most of the serious teachers I know became teachers, it wasn't just to sit on the mountain and dispense wisdom, it was so they could keep growing. Some things you can only learn when you are teaching others. It is the other side of the looking glass.
Quite frankly most of what exists out there is utter garbage, so the very fact that you have these questions shows that you aren't one of the 2 year shodans ready to open the kuhrotty studio.
At some point you have to accept that you have something to offer. I see too many talented people who live in the shadows of their seniors. Respect for seniors is a good thing, but not when it starts affected your own sense of self-worth. Be confident, as you may already know, half the battle for looking competent is being the one who is talking. People give you the benefit of the doubt when you are at the front of the room and this gives new instructors the space they need to get their footing. Teach honestly, and say you don't know when you don't know something.
Now, you are in Japan and studying in your teacher's dojo. I can see your hesitation to open your own. First, ask yourself if you are truly ready to run your own SCHOOL. This is different from teaching your own classes, and it is also where many would be Sensei fail miserably. Rent, insurance, utilities, managing the checkbook, etc. all business stuff, particularly in an urban setting.
If your teacher has a shibu that may need more attention, it may be worth your while to approach him about this. He could use the help, you could use the experience out of the nest, so to speak. He could check in and not feel like you are jilting him. This is just a suggestion. Hope this helps.
Glenn R. Manry
---Iaijutsu, don't forget the doorman.