BJJER - Yes at the elite levels it's somewhat true but not exactly.
For instance. Keenan Cornelius is elite, he trains with who? One of the top grapplers in the world.
I can't think of another example where the coah MUST be better than his pupils. And to top it off, get on the mat with them every day and prove it to them.
Give me an example of a competitor who maybe is not elite, who is better than their coach.
Come on man...
You're using an example of a current Brown Belt world champ that trains with a Black Belt World Champ as your example?
Think about black belts that aren't head coaches at their schools where they train with a coach?
Do you think Rodolfo can't beat Julio Cesar Pereira?
Or Leandro Lo can't beat Cicero Costha?
Or Caio Terra couldn't beat Cesar Gracie?
Or Roger couldnt beat his dad/Renzo/Carlinhos etc
There are plenty of elite black belts that train under a coach who isn't a current world champ black belt