It's more that there tends to be a dip in the upper mids/lower treble, as a feature of the house sound or a characteristic of the transducer. Maybe both. After the dip, treble is present again. For some people, they hear that as dark, since there is less overall energy in the entire treble region. For others, they hear it is bright or peaky, since that dip can accentuate what treble remains. It's kind of down to personal preferences, the music one listens to, volume of listening, and a number of other factors. That's likely why there hasn't been much of a consensus on your question yet. A headphone like the Atticus has a more even FR through that area, but the level of the treble is lower overall and sweetened by the dynamic driver (all to my ears, anyway).