I wonder about this hypothetical/thought experiment...
Take two people, both very smart, academic/book smart and street/life/common sense/emotional intelligence smart. One is a 2.5 handicap, the other, not much of an athlete, but plays golf.
Both audit let's say 2,500 lessons given by a mix of say 5 different instructors who really know what they are doing. Both have read up in everything instruction wise - TGM, MORAD, SnT, 5SK, etc...
Having never instructed golf before, both give lessons to all sorts of players, let's say 500 lessons, under the tutelage of above instructors.
I think the answer you are wanting is that all things being equal, the 2.5 HC would do better because he understood the knowledge enough to implement it. If all things are truly equal, you might be right, but the thing that would have to be equal would be the ability of the teacher to understand the STUDENTS' swing, to compare it to what they are trying to teach, and to communicate the differences to the students in such a way that they are able to implement the necessary changes. Even if the student is starting from scratch, the teacher must be able to communicate the desired actions, observe the student's attempts, and describe what is right or wrong in such a way that the student understands.
Natural athleticism is a gift; I don't think it can be taught. I think you can work out and become stronger and/or more flexible. I know you can improve hand/eye co-ordination- golf actually did that for me. I think you can improve your skills at anything, but not everyone will become Michael Jordan or Tiger Woods, or even the least skilled player in the NBA or PGA. Teaching is also a gift, and some of the best athletes would make poor teachers. In golf, there are those like our illustrious Erik who are both successful teachers and very good players.
Fred Couples is probably my favorite golfer to watch swing, and a natural if there ever was one, but his description of the swing is, " I take it back, and I hit it, and that is as good as it gets."
I do think a teacher who is between the ages of say 21 and 60, with no physical limitations, should be at least a single digit, or I would doubt their understanding of the game.