The question was, who makes a good teacher. And my answer is, someone with something to teach AND the ability to teach it. There are many great musicians who have absolutely no idea how to explain what they are doing. Often the most gifted are the worst teachers because everything came so easily to them that they can’t conceive of anyone else having problems. But there are rare exceptions. Grandjany, Jamet, Borot, Renie, and many others were harpists of phenominal ability who were able to explain in detail how they did what they did.
I could(but won’t!)name several important orchestra harpists with important teaching positions who are dreadful teachers. Having an orchestra job is absolutely no guarantee that that person can teach and prepare his/her students for a professional career.