@Jim;
Interesting observation

I have only been through realtracks of the genres that had the style/sound I wanted, so I haven't actually listened closely enough to some of the other realtracks to notice the differences in brightness that you mention.
I AM actually getting a bit worried now that this is turning more into science than 'emotion'.
It's easy to get caught in the science parts of sound, and lose sight of what music is fundamentally about: emotions

But at the same time, the science part DO make a difference. A good song may get great if the brightness is spot on for that type of music, or a great song may be considered only 'good' if the brightness is off what it ideally should be.
Maybe it's true; sound-engineers and musicians need to be 2 different people, rather than being 1 person trying to master both disciplines.