A flat response for a speaker is always wrong. Especially in the bass. Not only does no one make a speaker like that, but audiophiles often have a preference for going towards one flavor or another. These are not laboratory instruments no matter how much audiophiles claim to want neutrality they hardly ever actually like it.
There are a number of well-researched curves such as the Harman or B&K curves which are not flat, and the research done in terms of bass levels. Flatness is wrongness. Even smoothness is something debatable especially for those who like to feel visceral impact of a plucked harp string.
The list misses ability to reproduce the acoustic space of the recording.