kenjit,
Like many of us here you also seem to be searching for definitive answers and ultimate truths when it comes to loudspeaker performance. Unfortunately, there may not be any.
Whilst it's always advisable to keep an open and inquisitive mind, isn't there also a corresponding danger of falling into the trap of excessive paranoia and suspicion?
From my point of view when a designer has spent decades looking at every facet of loudspeaker performance in as much precise detail as Siegfried Linkwitz obviously did, I feel compelled to pay attention to his words.
You need an example?
How about this one taken from his website?
N - Mounting a driver to a baffle
"There is yet another potential problem with the driver to baffle interface, even if the baffle is perfectly inert. It is related to the mechanical construction of the driver itself and how it can become a mechanical resonator of its own.
Typically a loudspeaker driver has screw holes in its basket for mounting it to a baffle. Usually a sealing gasket is placed between the driver basket rim and the baffle. The driver becomes in effect stiffly clamped to the baffle. This method sets up a mechanically resonant structure which is formed by the compliance of the basket and the mass of the magnet as seen in figure (A).
A) Drivers with a stamped metal baskets are prone to exhibit a high Q resonance when tightly clamped to the baffle. The magnet moves relative to the voice coil at the resonance frequency. Energy is stored and also readily transmitted from the moving mass of the cone into the cabinet.
B) Soft mounting the driver basket to the baffle using rubber grommets reduces the resonance frequency. A 2nd order lowpass filter is formed that reduces the transmission of vibration energy from the moving cone to the baffle and cabinet. The resonance must occur below the operating range of the driver.
C) If the driver is mounted from the magnet and the basket rim touches the baffle only softly, then the magnet-basket resonance cannot occur and the transmission of vibration energy into the baffle is minimized.
The basket-magnet resonance can be measured with an accelerometer that is mounted to the magnet. The drive signal is optimally a shaped toneburst. Its energy is concentrated in a narrow frequency band. When tuned to the right frequency a long decay tail becomes visible on an oscilloscope. Often the resonance can be seen as a small bump in the driver's impedance curve in the few hundred Hz range. It should not be confused with the higher frequency bump due to cone breakup.
An early example of a box loudspeaker where a KEF B110 midrange/woofer driver magnet is clamped to a support structure. The clamp can be tightened from the outside of the box. The basket rim is floating.
Often the effects due to driver mounting are deemed to be of secondary importance to the overall sound quality of a loudspeaker.
They are usually costly to remedy.
They cannot be ignored when the goal is to design a loudspeaker of the highest accuracy."
https://www.linkwitzlab.com/frontiers_2.htm#N