Tube amps are LOW FI , not HIFI, since 50 years
Talking about "fidelity" : tube technology is inferior to well designed SS technology, and deprecated since 50 years
Tube tech provide : high distorsion, high noise, high heat, low power, low reliability, high cost, non linear frequency response... Everything is worst in a tube amp (and please don't ask about even distorsion harmonics : these harmonics, as their name tell it : are relevant to distorsion... and there should be no audible distorsion at all in Hifi : so even harmonics are out of scope).
The only domain where tube is still superior is : LOW FI : mainly for guitar amps where high distorsion with majority of even harmonics and frequency response non-linearities are qualities, and high noise is not a problem, as well as low power on 15'' high efficiency guitar speakers.