Good points. With science and engineering text books, the latest methods, books and editions would seem the most current and best, accurate, etc. However, in the area of classical music, we are talking about faithfully interpreting music written one, two, three hundred years ago. The technique to play classical piano on the modern grand piano has been well established a hundred years ago.
In other words, we are talking about mature technology here, in engineering terms. That is why the best conservatories are staffed with teachers with lineage to old schools of classical music playing/teaching. Do people consider the current teachers and their methods of teaching better than that of, for example, Beethoven, Liszt, or Chopin, etc?
I would not say that we don't have great classical music teachers now. But to say, just because, some one/thing is from an older era, therefore it is out dated and bad? I don't think so, at least not for classical music, and incidentally, morality.
As for students who wish to learn Jazz, blues, pop, etc, I say many of the current method books are not the best direct teaching methods for that. I believe what most private piano teachers do for beginners is to give the students a firm foundation in music, based on the classical music. Then the students can explore the other idioms later, on their own, or with another teacher specialized in those idioms.
I believe what private teachers find the current method books attractive is for the purpose of the retention of students. A few beginner blues-like, or Jazz-like songs might hold that student that hates classical music (out dated), and wishes to quit. But are these students being taught blues, Jazz and the like by these beginner method books? I don't think so. For that reason, current method books do serve an additional purpose for private piano teachers, from a business perspective.