Loudspeakers in an infinite variety of rooms are so varied that evaluating other equipment only has merit in a particular system. There are exceptions, a cartridge that does not track well will break up prematurely and that will apply to all systems. Otherwise clearthinker is right, you can not generalize to other systems. Now if there was a calibration standard that could be applied to audio systems like there is for projectors this could change. This is actually now possible given digital control but would not apply to "analog only" individuals.
In short, we are very much all alone by ourselves when it comes to evaluating equipment. What sounds great in your system may not be great in others regardless of quality. This is one reason you have to take reviews with a grain of salt. You may also notice that certain brands are always being reviewed by people who are fond of that brand to begin with. Bias has many forms.
How do you keep from buying equipment that will not work well in your system? In the end you can't. I would bet that many if not most of us have bought equipment we became unhappy with. Our systems evolve slowly over time and we learn what works well with our own situation. Set amps will be worse than terrible with my speakers. I know not to go there. With horn speakers my amps are extreme overkill. There are so many ways to skin this cat. We all have our own ideas of what is best. I do find it interesting that if you have an excellent system evaluated by a number of audiophiles all will agree that it is a fine system. The same will happen with a terrible system. All will agree it is terrible. So there is a standard in our heads even if you can't define it.