Well, there's certainly a clearly audible difference listening through my earbuds which is nice if you're trying to demonstrate a difference. I think/assume the complaint about "auditioning" speakers via YouTube is it doesn't give you a realistic sense of what you're going to hear in your room.(?) I couldn't tell you which I might prefer in person, or whether I think the system as a whole sounds good or bad. I assume the tube amplifier is the top video and the SS amplifier is the bottom video. There's an easily audible difference regardless.
It's also necessary to voltage match 2 amplifiers when doing A/B/X tests not SPL match. We do it to +/- .003 volts with a 1khz test tone, though in this demonstration I assume the tonal shift is what you're demonstrating. When comparing similar amplifier types, even the tiniest difference in level will skew the results.