Hey Sean. Good question. I'll try to give my two cents on this.
It's hard to find a person that is the best at enacting something and the best at teaching something.
To be the best at teaching something, a person will have to have, not only a keen understanding of the subject, but be able to relay that information to an audience or individual, in the style that that audience or individual can comprehend. These would be called "The Best Teachers". They can be football/baseball/basketball coaches, professors at a university, a tutor of a subject, practitioners of martial arts. Examples of the best jiu jitsu teachers off the top of my head would be Gokor, Eddie Bravo, Sean Bollinger, Rafael and Gui Mendes, Denny Prokopos, to name a few.
The best instructors/teachers may or may not have been the best performers of that subject, but they understand the game, they see patterns, and they relay these patterns to those more capable to enact on the opportunities that the patterns lend.
Those enactors are usually considered the best practitioners of that subject. Let's look at Michael Jordan and Kobe Bryant as an example. They are arguably some of the best practitioners of basketball(the subject) of all time. Why? Was it their talent level? Yes. But could they have also been guided by arguably one of the best teachers/coaches of all time in Phil Jackson? Maybe so. Phil Jackson knew the game intimately, and he was able to find people that would enact his strategy(Triangle Offense), ultimately to win championships, over and over again.
So the best practitioners(superior athletic ability coupled with recognition of patterns and acting on them) may or may not be the best teachers. But the teachers need them to enact his or her gameplan, and a side effect may be that that practitioner becomes the best at what s/he does, in that era. Note that the practitioner will have repped the crap out of a technique or move, so that the game becomes a series of patterns, and when the time presents itself, the superior practitioner capitalizes on that instant in time, almost automatically, using finesse and/or sheer force. Marcelo is in that category of jiu jitsu competition best practitioners. I've never received instruction from him, so I can't comment on that part, but my guess is that he is also one of the best teachers as well.