Another point of consideration when comparing the USA and Europe regarding steam locomotives is the amount of time the operator is willing to let the locomotive sit while it undergoes routine maintenance.
As a rule of thumb, European locomotives were much more fuel-efficient and much more labor intensive than American locomotives but American locomotives spent more time working and producing ton-miles.
After all, a deGlehn compound may get more out of a ton of coal than a simple American locomotive but it isn’t producing any ton-miles or passenger-miles while it is sitting in the shop being maintained.
That’s true inasmuch American designs were comparatively more robust in the late steam era in that, for example, they had cast frames with integral cylinders versus riveted frames. The capability to produce such a large casting now in America, at least to my knowledge, is a “lost art” and that’s why many late era American engines can not be reproduced, unlike the A1 they are recreating in England from the frame on up.