Hi Jess,
Yes, I have heard some bright ones. I think if one does a check of the tweeter's frequency response (FR), one will see some things. Plus other possibilities.
1) Often there is a resonant peak around 6khz, depending upon the driver.
2) I have seen many tweeters, even expensive tweeters, with peaks around 15khz, give or take. Some have multiple peaks between 10khz and 20khz. That is a recipe for problems unless addressed.
3) The "reference" amp/pre/source, or room used to tweak a design may have contributed. For instance, if the amp lacks highs, the speaker will be designed too bright in order to compensate.
I try to test each component, individually, for accuracy in absolute terms. Even then the room will play a part, so I encourage adjustments on the speaker itself.
I have always been in favor of adjustments on each component.
4) I am only guessing here, but some may like the "air" that exaggerated highs would create.
I have heard some recordings, especially older LPs tended to exaggerate the highs a little. I would guess that is because of the inferior cartridge/needles back in those days, thus more wear created. Someone with more experience than me may wish to address if that is true.
Just some thoughts Jess.
Cheers
Steve