I hear the same but cannot think of any technical reason behind it.
Could it be psychoacoustic? Mids and highs are perceived differently depending on bass quality and vice versa. Not easy to conduct a clean test even with separate amps for each driver.
It also enhances non linear distortion caused by drivers. In this respect it is the worst solution already in theory.
Anyway it is not true that it enhances the low frequency response of loudspeakers by default. Because MOST loudspeakers are designed FOR high DF amps I would be surprised by the contrary!
If a loudspeaker is designed with a different approach high DF is likely detrimental....that's why it's hoax.
99% I don't think so, even with commercial speakers. Cheap experiment: buy a pair of old Mission M73 (I personally can find them in mint condition for just 100 GBP here in UK) and will see that any good SE amp with DF of 2-3 will kill any other amplifier...bass included. 😉
Correct me if I'm wrong, but this is not about damping, which is about response.. it is about linearity? So it is about Zo, not DF, despite them being the same thing. These two topics wouldn't seem to conflict with each other.