How to judge a preamp's sound


I just heard a YouTuber review a preamp. He told the audience that he tried it with many amps, and then went on to offer descriptions about "the" character of the preamp (bass, midrange, and treble, etc.).

My question is, Can someone accurately generalize about "the" sound of preamp across a variety of different amps? Wouldn't the amps be enough of a variable to at least complicate the "character" of a preamp? This is a serious reviewer with many subscribers.
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And also back then in those vinyl days it was a long held saying as well, "the best sounding preamp should sound like a piece of wire" or "sound like no preamp"
These two, 'sounding like a piece of wire' and sounding 'like no preamp' are not the same. The latter is good, the former is really variable!
I've always been intrigued by "sound(ing) like a piece of wire." Do we have wire listeners???

back then in those vinyl days it was a long held saying as well, "the best sounding preamp should sound like a piece of wire"

These two, 'sounding like a piece of wire' and sounding 'like no preamp' are not the same. The latter is good, the former is really variable!

I’ve always been intrigued by "sound(ing) like a piece of wire." Do we have wire listeners???

If anyone questions the implication of this classic statement that goes back to gramophone days, then sorry, there is no hope, "get out of the game" another saying, just in case😉