Well, I am being a little tongue-and-cheek because I think most metrics we would seriously consider would create some controversy so I am staying away from that actual argument. But yes, I think the first part of your argument would need to be some kind of declaration of what is successful teaching.
I am not sure I am debating learning science. 20 years ago it was clear that gym class was a waste of time for students in the US. 10 years ago it was a waste of resources to teach music. I think studies are interesting, but I think studies of the studies would be warranted before I would weigh in on the usefulness of any particular finding. I don't think there is anything wrong with individual instructors who explore different teaching methodologies if they translate into skills. I am still not sure we aren't just talking about a mis-expectation of performance. If I see a shihan who teaches a very advanced class that I can't follow, I am not sure that is a fault in "traditional instruction," in-as-much as a mistake on my part that I expected to learn something. Of course, that means admitting that I was in a class over my head...
And yes, none of what I say should be viewed as a free pass to be a bad instructor.
There are several comments in the overall thread that seem to be asking what constitutes successful teaching and how this should be defined. Maybe Bad Teaching is easier to define? Though the metrics might be the same.
Boylan Sensei, elsewhere on this site you commented on how the Koryu method was built on a close relationship between student and teacher - presumably teaching and learning styles having to get matched up? But, what I might have thought were traditional methods were really military methods. I was wondering if you could flesh out the differences between these two methodologies?