Brian Hollingsworth's book on express passenger steam locomotives offers some interesting insights into the regard in France for complex locomotives such as the de Glehn and later Chapelon machines.
Apparently France is lacking in coal supplies, so thermal efficiency was paramount. England went to four cylinder steam like the de Glehn designs, but opted for simple instead of compound operation because coal was somewhat more plentiful.
It had been suggested somewhere else that the reason that the Industrial Revolution (i.e. the wide spread use of steam power) happened in England and not France is that the early steam machinery was only marginally cost effective, but the abundance of coal in England tipped the balance towards using coal in steam engines (coal was a form of labor in that someone had to dig it out of the ground) over direct labor in the factories and mills.
Similarly, France is 80% nuclear on their electric grid. One could argue that France is "more progressive than we" on CO2 emissions, but the simple fact is that France went nuclear because they had to, much as they went for complex compound steam because they had to.
What is interesting from Hollingsworth's book is reviewing the stats, and on comparing US Superpower steam against some of Chapelon's creations. It seemed that Superpower needed about twice the weight, grate area, evaporative and superheating surface to get the same amount of "cylinder horsepower" as the French designs. I suppose if coal was relatively cheap and you wanted the weight for pulling tonnage, Superpower was a good design. But it is brute force in comparison.
Hollingsworth comments, however, that some post WW-II US-built Mikes they had in France were more cost effective than the best that Chapelon had to offer -- what they gave up in coal consumption, even at French coal prices, they made up in lower maintenance, although it was explained that the Mikes were that good because Chapelon had made some steam passage "tweaks" on them. Kind of like a big-bore V-8 with tuned headers being more effective than some fancy small displacement overhead cam multi-valve exotic European mill.