So when a tube amp adds even a few percent of even order harmonics our brains easily blend it into one seamless whole.
Solid state and digital however are not at all like this. The distortions they produce are far lower in magnitude
MC’s assertion that SS amps aren’t mindful to 2nd harmonics is complete rubbish. It’s simply a matter of how the circuit is designed. For decades Nelson Pass has placed a large focus on balancing the right blend of 2nd and 3rd harmonics into his designs, or providing amps with different harmonic flavors to the market. He’s stated in interviews that about 1/3 of listeners prefer 2nd harmonics, 1/3 prefer 3rd, and the rest prefer a blend or have no preference. MC loves to be categorical in the "truths" he pushes but often he is simply asserting a bias.