You just need to understand that measuring the voltage with a voltmeter when a sinusoid is applied, and this is exactly what is being done - the same benefit as measuring the mass and dimensions. This can be done easily, you can even use very expensive devices and get a lot of decimal digits, but the sense is about ZERO.
For example, a sine wave of -90 dB is not an audio signal, which means that it does not reflect the behavior of the system under study when playing music. For substantially nonlinear systems, the principle of superposition is not satisfied. That is, the response of the system to a complex signal is not equal to the sum of the reactions to the components of this signal. That is, one harmonic per sinus. Two sines - already 10 times more modulation products. 100 sines 1000 times more modulation products. The condition that the response to 1 sinus will be the same as to a musical signal is not fulfilled.
I am not opposed to measurements to identify technical defects. Indeed, the measurements of some AV receivers here show that someone in the development department needs to be more attentive to their work. But buying audio based ONLY on a measurement sheet in a box is the same marketing story as the signature of Peter Quotrup. That is all I wanted to say.