That’s it. It’s theory mixed with engineering without separating the two. Every scientist and engineer knows that they shouldn’t be mixed. His tests are meaningless. If you want to test your theory, your rig must be representative of devices that is expected to be used along with the amplifier in test.You seem confused about the point PMA is trying to make. Maybe you should make an effort in understanding the theory..
Any EE will know that an amplifier with feedback and load dependant output impedance is prone to issues. You can analyse those issues and think of various ways to stop them happening. The engineer then decides which option fits their design brief, budget priority or SOTA. Once the amplifier is built they then test it.
Anything else is what a hobbyist will post, which is fine until he declares an amplifier to be unusable. Then others chime in to say the same to the level of declaring the engineers useless, etc.
In my view those members have done a disservice to ASR.