But isn't it strange that the proficiency is that spread apart when it's the same techniques and you have a black beltb One who has likely done his fair share of Newaza by that point
Actually the range in throwing ability among judo black belts is even larger than the range of ne-waza among judo black belts. Why is this? Long story - here's the TLDR:
BJJ black belt means expert
Judo black belt means ready to be a student (ie have a good breakfall, can be thrown without being hurt).
But if you're bored, here's the reason.
For a start, consider physics. I use the same techniques as Einstein did. I have degrees in physics like EInstein did. Our proficiency (very sadly for me) is universes apart. Same is true for my guitar playing vs say Hendrix or Julian Bream - though we used the same techniques, and I've played a lot longer than Hendrix did.
Knowing a technique theoretically is different from being able to apply it under increasingly difficult conditions.
Its not just judo (or physics or guitar); how many BJJ black belts are as good as say Roger Gracie or Marcelo Garcia?
Beyond that, what does black belt mean? For Kano (an education prof at U of Tokyo), black belt meant you were ready to become a student (ie you had a break fall and some basic principles). That is why he made ten degrees of black belt - the first is like a grade one student, the tenth is a grade ten student (think education prof). Meaning, first degree black belt is a child who knows the basics of speaking and discipline, but can't read and write yet. Kano didn't come up with that btw, it was common in various Japanese arts long before him, he just applied it judo.
The 'expert' ranks in judo start in theory with the red and white paneled belts (6th degree and up), called the kohaku ranks. When judo came to the Americas (south and north), somehow that was lost, and people thought a first degree black belt meant expert (why have ten degrees of expert is a question that never occurred to anyone). BJJ took that impression, so for BJJ black belt means expert.
Then in judo itself the various degrees of black belt kind of became superfluous in most of the world (North America, Europe, Soviet Union) - ranking like that isn't really part of the culture. Wrestling, boxing, basketball - there are no ranks in western sports. So world champions wouldn't bother grading after the shodan, and you have first degree black belts who are world champion level, and first degree black belts who've only done kata, or taught, or just showed up regularly for years. Under Kano's system, the later would still be shodans (they have a break fall and basics), but the world champs would be high ranking black belts, but that's long since fallen apart.
In short if you're wearing a black belt in judo, I assume I can throw you hard without you hurting yourself when you land, nothing more. So yeah, there are going to be huge ranges in ability in black belt. BJJ changed the meaning of black belt from judo; nothing wrong with that, but you have to remember it means something very different in BJJ than in judo, and since judo used it first, it'd be silly for judo to change to the BJJ standard of black belt means expert.
