An effective teacher has a commitment to the student's undrstanding.
Instructors who stand in front of a class and demonstrate their technique with little regard for whether their students actually understood anything, are not teachers.
As to the different grades of teachers, an excellent teacher does have a "plan", but it is transparent to the student. The student comes to their understanding and abilities because the teacher has helped them discover their skills.
A fair teacher has a plan and sticks to it mainly by rote. They can get a large portion of their students through the techniques and philosophy, but they lose a good many students who do not understand.
A poor teacher insists on being called "Sensei", struts around telling their students that their technique is wrong, and make it the student's fault for not understanding.
In my experience, the best teachers have learned from their mistakes and are able to correct themselves in front of their class. I remember on different occasions Kobayashi, Sensei sharing his thoughts on a particular technique, not have the technique work the way he had been taught, then break it down into smaller units of movement until the error was discovered. I have found that this increased my own understanding many fold, and, it also modeled for me excellent teaching.
I realize that it is tempting to identify one's instructor and/or one's self in the above definitions.
My point is that excellent teachers are always so regardless of the material being taught.
Poor teachers rely on being "the teacher", not their ability to teach.
Fair teachers always have the lesson plan. They stand a chance of becoming excellent by dint of practice.
The martial arts have had two models, one allows for excellence, the other does not.
The one not allowing for excellence is one of "authority and student". In this model, the student must submit to the authority unquestioningly.
The one allowing for excellence is that of "master and disciple". While to outward appearances, this may look like the other model, it is not. A "master" actually knows and helps the disciple to come to their own "knowing".
Unfortunately, too often in the martial arts, the functioning model has been "authority and student".
I apologize for this long peroration, however, teaching is very important to me.