"A UT doesn't control the inharmonicity, if bringig together many perfect intervals it simply makes it irrelevant."
It's funny that we don't seem to have enough common language to discuss these issues without misunderstandings. I believe in maintaining the beat rates of the mathematical models when tuning actual pianos, ignoring inharmonicity to the extent such is possible. Not sure if you are saying a similar thing.
"If the UT has a number of perfect fifths arranged so that there are some perfect thirds too, then there will be a lot of mathematical concordance in the vibrations produced. That harmonises.
That is true. But we differ I think on whether temperament should or should not be considered a zero sum game. In UT's the concordances in some keys are the direct result of making discordances in other keys. In my world, professional pianists are working on spinets, play in all keys and are accustomed to a nice pure 12th ET. Just like UT's, pure 12th ET plays a zero-sum game because the concordances of the 5ths, octaves, and 12ths come at the expense of tempered M3rds just like in pure octave ET, but this is a solution with a solid history. As long as there have been modern pianos, there has been stretch; pure 12th ET stretches in quantity about the same as traditional stretch; the difference is that the stretch is carefully controlled to be uniform through more than just the middle 3 octaves, one might claim it is uniform through the whole scale. When combined with high precision tuning technique, and after a good bit of practice at it, the effect can be heard by many laymen as a very, very good tuning. You continue to mention the shimmer of ET, but I hear purity and coherence and consonance in every single key with the modern ET's
"If the central three octaves in which most harmonic activity is set up are tuned without stretch, then the fundamental of many of the scale notes will interrelate in exact mathematical accordance."
I don't see the way in which this statement could be true. If one tunes the upper note of an interval to sharp partials, then the intervals as measured at the fundamentals will be wide to the mathematical model and will not "interrelate in exact mathematical accordance". Really wish we could reconcile this language; it would be worth the effort.
"By doing this, the inharmonic partials are sent all over the place, not reinforcing each other. So then the harmonicity of the scale overcomes the inharmonicity of the strings making the inharmonicity irrelevant."
This sounds to me to be a description of chaos, not coherence, dissonance not consonance, and this could be readily heard as such.
You know, you and I share an interest in Pianoteq. Maybe we should share some short demonstrations of the effects about which we speak, recorded with Pianoteq. We could even develop MIDI files to be played with each of our preferred settings in A-B fashion.