Indeed - and you do see a little
US<->UK jingoism pushing some of the facts out of the way in that discussion.
The truth is that all reciprocating aero-engines need supercharging to perform at high altitudes. The only open question is: shall it be a
mechanically driven supercharger or an
exhaust driven turbosupercharger (in those days, electrically driven "
e-chargers" were not an option).
The turbosupercharger worked fine - when it worked - but the design of the necessary ducting and the exhaust turbines and of the intake boost impellors is really complex and the metallurgy of making something like a turbine stay together at those high temperatures was also non-trivial. Also, all of this additional hardware was bulky (P-47) and heavier than a well-designed mechanical supercharger like was available on the Merlin and the German DB601 inverted V12 plus several other German Vee and radial engines made by Jumo and BMW.
The US did eventually work it all out very well -
juuuuusssttt in time for gas turbine engines (
aka turbojets) to take over and eliminate the market for large capacity piston aero-engines. That was why one saw the golden age of piston engines like the Wright
R3350 TurboCompound and big Pratt & Whitney
R4360 Wasp Major really come-on strong in the mid-late 1940s-1950's - and then largely disappear by the early 1960s.
The other thing that gave turbosuperchargers a bad reputation during WW-2 was that while the US did have workable technology, due to security concerns in 1939-40 it would not usually allow even trusted Allies like the British to buy it. So, when the UK evaluated the Curtis P-40, Lockheed P-38 and the Bell P-39, they were stuck with
un-turbosupercharged versions which were complete dogs above about 10,000 feet. The Allison engines were fine and the airplanes were good - but without turbosuperchargers, they simply could not compete in the European theatre.
EDIT: As for the North American P-51 Mustang, it was originally designed for the British (not the US) and so as an export product, it was not eligible to have a turbosupercharger installed - and so after a few Allison-engined versions were built, they installed a Merlin with a mechanically-driven supercharger and
WAH-LA.
Anyhow, thank goodness for the R-R Merlin and Sir Stanley Hooker....