Your absolutely right. Preamps have their own characteristic sound. When I did a demo in my first home system with 3 preamps before I purchased. All were on my turntable and speakers in my room. What matters is what type of sound do you like and are you happy with it. The three power amps also were different. The right combo was the winner.
Preamps can color sound considerably. Surprising?
Had the pleasure of listening to 4 hi end preamplifiers this weekend. And each preamp sounded very nice. But they were different. Each preamplifier has different circuitry and within the frequency spectrum there was more vibrancy in some areas versus other areas. Amplifiers are the same way.
It takes a while to appreciate sound differences between preamplifiers. And then you got the issue of Breakin which further changes the color.
clearly designers are playing around with all the internal circuitry in a manner that hopefully will be appealing. Clearly, these units do not get out of the way when it comes to moving a signal through the box.
I think solid state is more susceptible to coloring versus tubes. Tubes color sound as well.
It's all about marketing different ways to color Music. This isn't necessarily bad but it's never really talked about this way.