I don't know how the downmix for headphones is created in this case, but if it spatializes the individual objects correctly, this removes the in-head-localization artifact that unprocessed stereo on headphones suffers from naturally, especially for sounds with a center pan. We have just trained ourselves to accept that headphones make sounds appear inside our heads. And I am pretty certain that the author is mistaking the acceptance of this artifact for a "prominent presence" of the vocals in the demo tracks.

Listening to a track that was intended for a stereo loudspeaker pair on headphones always creates a degraded experience if there is no further processing of the audio signal. Judging spatial audio without consideration of these differences leads to weird (wrong?) conclusions.

And why does it matter how expensive a certain pair of headphones is? If I want to know the price tag I can look it up!