It fits with their other examples much better.
That doesn't fit OP's thesis at all.
Take the 2-8-0, which https://en.wikipedia.org/wiki/2-8-0 comments:
> From its introduction in 1866 and well into the early 20th century, the 2-8-0 design was considered to be the ultimate heavy-freight locomotive. The 2-8-0's forte was starting and moving "impressive loads at unimpressive speeds" and its versatility gave the type its longevity. The practical limit of the design was reached in 1915, when it was realised that no further development was possible with a locomotive of this wheel arrangement. ...
> During World War II, 14 of these locomotives were equipped with superheaters, which raised their tractive effort from 28,777 lbf (128.0 kN) to 33,557 lbf (149.3 kN)
Then compare to https://en.wikipedia.org/wiki/EMC_E3 , a diesel from 1938 with "Tractive effort Starting: 56,500 lbf".
That's from time when people became convinced that diesel was better than steam. Why? Quoting https://www.american-rails.com/diesel.html
> This changed after General Motors successfully demonstrated the diesel's viability during testing of its FT freight design in 1939.
> The demonstrator set toured the country, convincing skeptic after skeptic that diesels were not only efficient and reliable but could also outperform the iron horse.
Not simply because it was dirt cheap.
Stats at https://en.wikipedia.org/wiki/EMD_FT . The top speed of 95 mph is 15 mph higher than the Union Pacific Big Boy.
Note also "Steam locomotives could be built with fewer precious materials, and with less conflict with military needs.", which is yet another factor that OP's thesis didn't consider.
Did you catch things like "no further development was possible with a locomotive of this wheel arrangement" and from earlier "the six cylinders could easily consume more steam than the boiler could produce". These designs were pushing the limit of what steam could do, and diesel looked like it could pass those limits. And did.
Am I missing something? It looks like hundreds of diesel-electric locomotives are more powerful than the most powerful steam engines ever made.
I went to https://en.wikipedia.org/wiki/List_of_largest_locomotives then sorted by tractive effort/force and looked for the most powerful diesel and most powerful steam.
EMD SD70ACe-T4 - diesel-electric - 200,000 pounds-force (890 kN) starting, 175,000 pounds-force (778 kN) continuous - https://en.wikipedia.org/wiki/EMD_SD90MAC (478 built)
GE AC6000CW - diesel-electric - 188,000 pounds-force (836 kN) starting; 166,000 pounds-force (738 kN) continuous - https://en.wikipedia.org/wiki/GE_AC6000CW (317 built)
by comparison:
Erie Class P-1 - steam - 176,256 pounds-force (784 kN) - https://en.wikipedia.org/wiki/Triplex_locomotive (10 built) ("high tractive effort, but low speed, about 10 mph, over short distances" .. "the Triplexes produced huge amounts of tractive effort (TE) that may have been the highest of any steam locomotives before or since").
XA Triplex - steam - 166,600 pounds-force (741 kN) compound - https://en.wikipedia.org/wiki/2-8-8-8-4 (1 built) ("unable to sustain a speed greater than five miles an hour, since the six cylinders could easily consume more steam than the boiler could produce")
Power isn't the only factor. Steam engines produce the most power when just starting, which helps explain why the most power steam engines were also so slow.
(Something like the Union Pacific Big Boy had less tractive force, at 135,375 lbf, much higher speeds, topping out at 80mph. https://en.wikipedia.org/wiki/Union_Pacific_Big_Boy)
Going back to your thesis, in researching this I came across the Kaufman Act, at https://en.wikipedia.org/wiki/Kaufman_Act , which banned steam engines in New York city due to pollution problems. Originally it required electric propulsion, but was amended to allow diesel when that proved viable, and that in turn provided a stepping stone toward dieselization of US trains.
Diesel trains are not worse polluters than steam, so your thesis doesn't really seem applicable.