Brazilian Jiu-jitsu black belt cannot be legally obtained (in serious classes) without at least 5 years of being ranked as lower belts, and generally being active.
In practice, most averagely talented and training people will reach it way later, if ever.
And Judo ranking is pretty strongly tied with BJJ, and similar.
So it depends on art, but in those, for example, black belt has nothing to do with "basics" generally.