For me the first thing to come to grips with is what do I feel the black belt (BB) means in my school or for my students. Back in the 80's when I started being a BB meant something. Generally you would be accepted in a school or work out group as a person who knows something of value, there weren't young kids as BBs, Ernie Reyes Jr. being a young BB was an oddity, something you didn't see everyday and especially someone who had a such a high skill level. But today it seems like schools pride themselves on you can produce the youngest BB, or for that matter the youngest master or high ranked BB. It's crazy. So in a sense the BB rank has been diminished on one hand due to this type of an attitude.
Nowadays for several reasons a BB coming into your school isn't such a big issue it's almost like everyone has one, so because you are a BB in some system doesn't mean as much if you are not from that school, style, governing body or that system. That actually helps to free up the high expectations that we had in the 80's and I think ultimately gives the instructor more freedom as to what the BB means in his particular school. So as I set about creating a curriculum for my school I tailored it towards the more SD side of things, while still keeping the "martial art" through forms and basics. So I then set about adding in different drills, techniques, concepts etc. etc. that would tie the kata to basics, to SD etc. etc. and de-emphasized the tournament focused stuff.
So even with students who have learning challenges, I can make allowances for not having the kata exactly right (look wise) if the student is understanding some of the applications of the moves found within the form. I do this by teaching, asking questions of the students etc. etc. to gauge their understanding and I look to see improvement of their techniques as they train. All of this depends of course on the student, their age, skill level, attitudes etc. etc. However I try and set a decent standard that has both physical skill and understanding as part of it.
At my first BB test for my TKD students, my sensei was there and he said "Mark, I your kids did fine. I could pick apart their kata, their sparring was OK, but their SD they got an A on, and that's what is important" That was what I wanted to hear. Because his students do different kata, they also take a lot longer to get to BB, he has better instructors to help off set his teaching etc. etc. so they have in a sense more resources where I'm a one man show. So I wanted to pass onto my students more of the physical SD related material than having perfect kicking techniques or forms.
To bring this back around to the original discussion about what is the difference between a 6th dan and a GM, this is part of the reason I try and stay away from making comparisons based on physical traits or characteristics of the instructors. Simply because I suck at exams, I suck at tournaments, I don't kick like I use to, I don't look like I use to, put me up against some instructors that I know and I would look like the lower rank. Put me up against some of my sensei's younger BB students and have us do a kata and I'd look like the 1st dan.
However put me up against them with a weapon in my hand and that is a different story altogether. On my 1st dan test in Kobudo, I put in a lot of outside time getting ready throughout the whole 2 1/2 - 3 yr program. Weapons were my main interest and focus of study. It comes test time and I had carpal tunnel issues with my hands, I drove 40 something miles in my wife's mail jeep through heavy construction traffic, and I had just completed teaching about 3-4 hours of class prior to leaving for the test. Did I mention that I suck at exams on top of this. Worst test of my life, first time I ever blanked out completely forgetting a kata, dropped my tonfa during a kata cause my hands opened up due to the carpal tunnel, oh and I was one of the highest ranked (there were two of us at 6th dan) testing with a bunch of 4th-1st dans and some brown belts. Talk about humiliation to say the least. Out of everyone there I had the most experience (except for the examiners) with weapons due to my FMA background, all things considered I should have Aced it instead I stood their believing that I was going to fail my first test in 30 years of training. When it came time for one steps with the weapons I didn't care anymore and just let go since I was in my element. I had fun. I figured I was going to fail so I didn't worry or care at that point, it just didn't matter anymore.
When it came time to promote the senior instructors spoke about how at times we have bad tests for different reasons but we earn our rank on the floor, in class and outside of class. They knew me, they understood what happened, they looked beyond the two hours of the test and instead took into consideration the many many hours that I spent outside of class teaching my students the same material and practicing it. So they passed me and used it as a teaching lesson to the rest of the students.
Had someone like, I feel some of the posters here (I don't mean personally but more from the tone of some posts) seen that exam, and seen my rank (even though I don't wear stripes on my belt

) I'm sure I'd be mentioned on some internet forum as a fake. I'm sure some of the people testing who didn't and don't really now me wondered WTH? How could he pass? He forgot a kata completely, his tonfa flew out of his hands during Tonfa Ichi, they might get disgusted and leave the organization or feel I bought the rank (for all of $10.00 for the regular class test fee). Bottom line that was almost 5-6 years or so ago and I'm still there teaching, training and contributing. Where are they? Most of them aren't there. Out of the 100 or so people that went through my class 2010-2012 and the one after 2012-2014, there are maybe 5 from my class, 7-8 from the class after that are continuing to train for 2nd dan.
Whats the difference between a 6th dan and a GM, the 6th dan still trains and the GMs are the ones guiding them.