In any sport or skill, be it football or pottery, - you need a _better_ opponent/colleague/team mate if you want to learn, to progress. If Maradona or Ronaldo spends 10 years playing football with kids - most probably their own level will fade.
And here a dilemma arises for high ranked students - if I want to progress myself, I should stick to students with higher rank than mine.
I'm not really convinced that's true, at least that's not how it seems to work for me.
Of course if you practiced only or primarily with people less experienced than you, OK, I see the problem.
But as a supplement to training with more advanced people? I think it's great.
You are forced to look more carefully at everything you do to be sure you're not inadvertently teaching them something wrong or sloppy, you have to understand something more clearly and precisely and not just 'get the general idea' if you're going to show someone else, they ask questions that make you think and try to find patterns that you half-understand and figure them out more clearly so you can better explain them to the other person, and of course you learn how to make things work on people who have no idea what you're trying to do and who 'move funny', and keep enough control not to be hurting them.