One point only lightly touched on is the experience of the instructors. Many pilots are trained by instructors who only became qualified CPLs/QFIs a year or two before their students. The commercial schools even hire newly/recently qualified pilots who were themselves students at the same school.
One of the most important qualities for good instruction is a deep understanding of why we do things the way we do them. A lot of this comes from experience, otherwise it is all monkey see-monkey do which is not the best stance from which to learn a profession which has a tendency to kill you if your awareness and understanding are lacking.
For credability, good habits and high airmanship, it is preferable to be taught by someone who has actually done the job for a while rather than a tyro who only got their license shortly before the student starts training
.