With respect, I disagree. Part of any keiko is to follow instructions; teacher says do irimi-nage, you dont stand there and say "No, kote-gaeshi would work best." (of course you may think that, just dont do that).
I personally know of a 6th dan who teachs, by his own admission, a student who is his senior in years of training and ability though not in rank. Shihan said teach class, so the 6th dan student does as he is told.
Beer: agree, but after, not instead of, training.
In this case we have 5th kyu
This guy don't even know how to walk correctly, everything
what he does is wrong even if he is very gifted and has black belt in judo/tkd/MMA whatever....
So you can't compare it to the relation shihan-6th dan instructor.
Believe me a beer is the only option in such situation.