Thanks for the laugh. I recall thinking when watching an aikido lesson: okay the teacher (who had 20+ years of aikido and of other martial arts) could use his aikido knowledge in a fight, the other(1) definitely not! And it could even be dangerous if they believed that they could use their aikido knowledge to fight, not that this is unique to aikido..
The concept of a black belt has been horribly twisted. It really just means some level of mastery of the basic techniques. It's meant to be a beginning, not an end.
It's like saying someone can take a class and earn some networking certificate, and from that point on they are an undeniable expert in networking. Of course that's ridiculous; that certificate is meant to certify a basic level of knowledge that is enhanced through experience, not complete mastery.
I heard that originally, you put on a white belt, and you just bled and sweated on it and got pounded into the dirt with it until it turned black with the accumulated filth of experience. Then you were a black belt.
1: even those of who were black belt