Regardless of whether it was a myth or not, how it was done was the right thing to do. The US manufacturing industry was way ahead of the UK in civil transport aircraft; setting aside the big flying boats the UK immediate pre-war landplane airliner production was completely outclassed. This was a combination of little demand, poor designs, and especially bad production standards.
You'll notice that these attributes continued in many of the Brabazon Committee's designs postwar. It wasn't until the Viscount that British industry appeared to produce a sensible airliner.
Military aircraft were different, even before September 1939.