I used to think that there was some utility to microphone recordings of loudspeakers played back through Youtube. Then I saw a couple of videos where two microphones were set up to record simultaneously. The differences between the two microphones recording the same playback at the same time was massive.
Microphone/loudspeaker pairings are potentially more significant than loudspeaker/amp-preamp pairings. Sadly, I don't know that one can judge much from the Youtube comparisons, as entertaining as they may be.
If the audio is coupled with comments about perceived differences listening live, it then comes down to trusting the commenter. I think in very controlled cases it might be possible to illustrate differences between speakers where the presenter/commenter/reviewer can say "I hear this difference listening in person, and it comes through in this recording." I don't think that has as much value when only one loudspeaker is being discussed.
In the case of the video, the rooms and source equipment are different so there is even less useful information. As entertaining as it is, there's just nothing to base an opinion on. The presenter says he has another video discussing his impressions, but he still hasn't heard the speakers in comparable settings. Still, it is entertaining.