Everyone makes good points here, and I will admit that it's pretty easy for someone like me to forget that there are a lot of good mentors out there. Heck, there's a lot of good ones in my own FC. XD
The sad thing is that this question spawned from two different things: 1) The way Square takes feedback for the game: post something on the forums, and 2) those people who have chosen just to get the crown symbol as a status icon or just to start farming for special things, among many other reasons. I've ran into a few bad mentors myself, and I've taught people mechanics better than what those mentors could. It's just sad though that the good mentors don't get a lot of recognition.