As whirly says, the major limitation of the current instructor course is that it doesn't really teach dealing with people. In the commercial school that that I taught at, the FI course for trainee in house instructors (modelled on the CFS course) was 63 flying hours. The main difference was that all exercises (including EOL's) were flown mutual as instructor and student. At least you learned something about how people reacted to your teaching technique with someone other than the FIC. However, who would pay the astronomical cost of such a course these days.