I'm going to turn the issue sidewards and ask some questions...
If you have been training for twenty years, does it matter if it took you the first six years to get to start wearing a black belt or just the first two? How has the journey been any different? Is is the belt you wear that changes the journey? Or the fact that you have been training hard for tweny years?
If you are attacked on the street and have to defend yourself (not out of bravado or over-inflated ego but legitimate self-defense), and you have been training for three years, does it matter if your belt is black or red or green or white or just that over those last three years you have trained for this possibility?
There is a school of thought that a Black Belt is where the training really begins and everything before it is just learning the moves of the art. I've heard that used by people to encourage others notto give up once they reach Black Belt, to treat it as a point along the way of training but just a point. The Black Belt isn't the goal to signify the end of the journey, but a new beginning, the real beginning in many ways. Turn that idea around and say that if the black belt is the point of serious training to begin in many ways, then whether you have a working knowledge of a technique or a real mastery of a technique by the time you reach that point probably isn't really crucial if you carry your training forward beyond that point.
I think where it starts to matter is when instructors start taking the rank itself seriously as a source of comparison "I won't promote anyone to black belt until they are such and such..." but who's going to care other than other school instructors? In purely practical l matter of what a given person can do *today*, their conditioning, their ability to defend themself, etc..
So take out the issue of rank completely and just think of it from a purely educational point of view, and to go back to Gemini's original question, I think *both* methods of education are valid. You can drill addition until you know addition forwards and backwards before moving on to subtraction, or you can do a little addition, a little subtraction, and build ont that as time goes by. At the end of the year, you know addition and subtraction...which was the better way to get there? They both have validity. Do you teach the mechanics of a major scale and the mechanics of a minor scale before develing into the theory of how the scales work? Or do you teach the major scale and thoery completely before encountering the minor scale? Both will work..*in the end*. At any given point along the journey different people who have approached it different ways are going to have a different set of strentghs and weaknesses...but if you put your best effort into whataver you were doing to get you to the point in time....
anyway, I have to run. Too much of this question seems to have been taken from the point of view of 'black belt' as the ending of the journey so whether it took you two years or ten years to get to that point means what kind of person you are. Try to think of it as a life long journey...try to think of it like that 1st grade teacher teaching arithemetic who will never see if her students bcome physicists, try to think that you are helping your students along a long path, some or much of it you may not see be there for, and think about how to best prepare your students for that journey
Just thoughts from a non-instructor and a non-black belt