Never have I read or heard a more ridiculous statement. i agree that if you find something difficult you will have more empathy with others who also struggle to learn. However you cannot teach something that you cant do.
Albert Einstein the most iconic scientist in history was reputed to have said “If you cant explain something( I think he meant Relativity) to a six year old you don’t understand it yourself. ” This suggests to me that a teacher has higher comprehension than those that don’t teach.
It is probably more accurate to say that if you can do something well you are unwilling to teach it. This would be the result of impatience or that the earning capacity is greater in the doing than the teaching.
Sports coaches might not be world champions at their discipline but if they coach world champions they are or were very good at their sport. Modern society has put teachers down as a default profession for those who haven’t made it. I have, for one have learnt masses from gifted teachers who really knew their stuff.