No, it's actually dips and peaks in frequency range that make headphones sound unnatural. It's like, when you talk about treble, you get for instance two peaks here, three dips there, and though you hear that the headphones are actually balanced, the timbre of the instruments is off and you don't believe the sound. It's not like being on the bright side actually hurts the realism, it's the treble not being flat enough that does (and all the other frequency range of course).
Takstars are definitely a bit on the bright side, but I think it doesn't hurt them heavily. The uneven treble does.