Oh come on now, that's obvious bullshit. The term "sound barrier" doesn't predate the 20th century and was only popularized during WWII. Any physicist claiming it was a fundamental limitation would've needed to be completely ignorant to the existence of artillery. Who were these supposed physicists and what specifically did they claim?
https://en.wikipedia.org/wiki/Prandtl–Glauert_singularity
> The Prandtl–Glauert singularity is a theoretical construct in flow physics, often incorrectly used to explain vapor cones in transonic flows. It is the prediction by the Prandtl–Glauert transformation that infinite pressures would be experienced by an aircraft as it approaches the speed of sound. Because it is invalid to apply the transformation at these speeds, the predicted singularity does not emerge.
> The incorrect association is related to the early-20th-century misconception of the impenetrability of the sound barrier.
I learnt about it from Destin's video: https://youtu.be/p1PgNbgWSyY?t=816
Likewise today, we know something is wrong with the combination {relativity, quantum mechanics} because if our formula for both were completely true, the universe wouldn’t exists.
The supersonic munitions of the era were rather difficult to ignore, so you need better evidence to claim PhDs would’ve laughed at the idea, than merely that the best formula they had at the time was not good enough.