I've read that quote, but have seen things work differently several times, so don't think it holds water. I also don't see how it is physically possible for the breech to open under pressure unless the extractor overrides, and then you would have a jam-o-matic.
In my food for thought thread in the 10mm reloading forum, sd dropped quite a bit with heavier loads. In the 10mm recoil spring video there was no clear trend either way using hot ammo. If the breech caused the velocity swings there should be some sort of indication in the brass, like it stretching .1" or a bulged casehead or a broken shell, since we are talking about the slide retreating a significant amount while under pressure.
A better test would be one that showed sd dropping as you went from firing without recoil spring, to stock spring, to heavy spring, to holding the breech closed, or at least a clear delineation between inadequate and proper support.