Al, as always, I appreciate your perspective. Thank you.
I do not consider 0 wpc an endpoint because the only time a tube amplifier, regardless of triode, UL, or pentode connection, would (practically) meet that figure is when it's shut off. And, of course, at that point, all three would be at 0 wpc. No, the lowest we're going to see in this example is the triode's 20 wpc, so that figure represents our lower boundary.
At any rate, I do not disagree whatsoever that a UL connected amplifier can make "most" of the power of pentode - "most" adhering to your strict (and, I believe accurate) interpretation of the word. In fact, it can go far beyond that, and achieve the "great majority" and "nearly all" meanings as well. That's no trouble at all; it's been done countless times.
The rub comes when the statement is made that we can meet that measure AND "approach triode linearity" at the same time. Impossible. It's akin to both ends of a playground see saw being up at the same time. Obviously, one side has to be up, the other one down, or both can be level with one another. In other words, as I've stressed, there is no free lunch. To believe anything else is fantasy.
Of course, in the strictest sense, the term "approach" can be taken to mean, even to the slightest degree, and by that I mean, 0.000001% of the way, let alone half the way there. However, in the context it's been presented, I've taken this as "most" (IOW > 50% of the distance between the two endpoints). Perhaps, that is wrong, and I've thus far happily waited to be corrected there. But I believe we need to be extraordinarily careful not to present a technology proposed in 1951, and adopted as the de facto standard not longer after, as possessing any unexpected or even mystical advantages - enumerated in the preceding paragraph or otherwise. When it comes to UL, most tube amplifier manufacturers of the modern era have been there and done that. Indeed, even tube amplifier designers who didn't believe in it were literally forced (in such entities, engineers and scientists work for the business area, not the other way around) to build such designs by the sales and marketing folks of the time.
Surprising as it may be in this thread, you might tell from my correspondence with Mike that I'm not at all opposed to UL operation. In fact, of the eight commercial high-end audio tube amplifiers I own, all but one feature UL. And that last one does not only because it uses the 6AS7G triode tube. As I said, UL has ruled the day in high-end audio since the 1950s. If I were to raise any criticism, it would have nothing at all to do with that which has thus far been discussed here in this thread; power and linearity. But I don't believe we're ready for such conversation until we level set what UL is and is not.
