Eric Greenwell wrote
If we taught them this way, we would be doing the student a disservice,
even if they never flew any other glider. It's widely understood that
you have to teach turning stalls, as these are the most likely way a
pilot will encounter a spin or spiral dive.

Maybe not as widely understood as you believe.

All I can tell you is this - spend some time as a power instructor
finishing up the training of students who started with typical power
instructors, or do some BFR's for power pilots, and you will quickly
realize what I'm talking about. Many if not most power pilots have
not a clue about why we do stalls or how to do them in any other
manner than the one I've described.

The average quality of glider instruction is DRAMATICALLY better than
the average quality of power instruction. I suspect that no small
part of this has to do with the prevalence of single seaters.

Michael