I personally think using the word 'stupid' in this specific discussion is not particularly useful, or relevant. Bulleid had Moon's ear; Moon had the money to build them; the basis of the argument is that British war-priority production would (or as argued "should" have made resource allocations for these locomotives differently, via some perception they were not 'true dual-service capable'.

Such a claim could be made, but it would require enormous amounts of data and knowledge that this community likely does not currently have, and likely couldn't afford to engage to provide. My own supposition is, indeed, that strings were pulled to get it to happen; it is difficult to explain the construction of the Q1, all the Q2s, and greenlighting of production of the original freight version of the V1 mechanical turbine all during the WPB era that supposedly so affected so many other railroads without recourse or, sometimes, apparent sense.

As I recall, part of the argument for the various Bulleid Pacifics was that they involved less use of strategic materials -- copper in particular -- and that some of the ingenious details of their construction made them more reliable in prospective wartime conditions, and less liable to be out of service unexpectedly. (As we know with 20/20 hindsight this was near-utterly ridiculous, but those who allowed the mass construction didn't or couldn't understand the details, or took them as Moon did on faith in Bulleid's expertise and ingenuity.)

While we're all in this wheelhouse, the real stupidity in my view was the postwar government's decision to throw over 500,000 pounds at the increasing kludge that was Leader, hoping to pull out a technological English tour de force of cutting-edge technology to match the Brabazon or other projects that channeled that Lucas vibe sooner or later. (Note how carefully I don't put Comet in that category -- it isn't oversight.)

As you say, Comet does not fall in that category-it was indeed a worthwhile investment and attempt to regain influence in commercial aviation. The failure there was strictly a design issue. The British aviation industry threw every resource into determining the cause of the Comet losses and correcting them quickly-so quickly that the issues were corrected by 1953 and the Comet 4 entered service at the same time that the first US jetliner (Boeing's 707) entered service. Had Comet 1 not had that design fault, the British could well have achieved the dominance in civil airliner manufacturing that they had desired.

That is precisely the point.

In a sense, the Concorde project represented just the same groundbreaking sort of engineering, in a much wider range of disciplines than most laymen probably realize, in order to produce what was in the Sixties the 'next step' in commercial aviation. A very similar achievement on the 'military' side was observed in roughly the same time period with the CF-105 Arrow development in Canada. It is interesting to consider how the market for multiple-supersonic aircraft would have developed in the absence of fuel and 'ecology' concerns -- personally, I think Concorde was too small to be a long-term practical alternative to projects like the 2707 or the adaptation of the B70 and scaling it to higher capacity wouldn't have been either engineering- or cost-effective.

Incidentally a cavalier attitude toward security was responsible for a couple of true disasters: the 'Concordeski' on the one hand, and Diefenbaker's abrupt termination of the entire Arrow project on the other. At least Boeing and North American had military paranoia rolled into their corporate DNA...

The stillborn British thing I loved the most, though, was the Fairey Rotodyne. We look today at operational models like those for zunum; the Rotodyne offered similar multiple utility generations earlier -- all that was necessary was some better mufflers. But then again exactly the same thing could have been said of the FG9. There's just a little more to get the noise-reduction achievement to actually work...

If you are going to mention the Avro Arrow, you mustn't forget the TSR 2......
https://en.wikipedia.org/wiki/BAC_TSR-2
Another "World beating" aircraft that was killed off.
We never even obtained the F111's that were supposed to be bought take its place in the RAF!

The problem with the TSR-2 was that it was like a really good F-105, or perhaps more an F-108: a very fast, large strike aircraft that in an era going to ballistic and then cruise missiles had relatively little alternative use. With relatively few alternative uses

May I suggest the Hawker P.1154 as a better example of something that should have been further pushed?