Don, I certainly hope I didn't offend, and in fact I'm glad if my comments played a role in prompting you to contribute such an interesting and erudite post.

The technique of using the left thumb to fret the bottom string is, as I understand it, pretty much verboten within the realm of classical technique, which requires that thumb be kept well down ast the center of the neck. The classical hand positioning maximizes your reach up and down the fingerboard, of course, but absolutely requires that barre technique be used for chords like the F major.

The inelegant left-thumb wraparound does pull your other four left-hand fingers back into a position where they can't reach nearly so far, but (in a few cases of really advanced ragtime/blues tours de force) it's the only way to play five strings at once at different frets, and to play certain runs of treble-string melody while holding down the requisite bass notes.

I'm able to play barre chords, and routinely play certain chords either with the thumb or as barre chords depending upon the context. Back when I was learning, however, I wasn't able to play the barres at first, and the thumb technique allowed me to play more chords sooner than I would otherwise have been able to finger.

(In general, I still find it easiest to play the F-major are related chords with the thumb, But I use barres almost exclusively for the Bb-major "family" of chords and for most of the minor chords.)

And Ted, point taken. I think we agree that virtually everyone on this forum who favors the classical guitar and/or classical training is someone using that instrument and applying that technique to a wider range of musical genres than strictly classical music. (Ted and I have a long history of minor disagreement over formal musical education versus an intuitive "by-ear" approach, but I do certainly respect his knowledge, and on more than one occasion I have depended on his expertise to learn a tricky chord progression or some other such musical subtlety.)