That is not the main factor in determining a good monitor for producing. More importantly that comes down to your over all mix how something is going to sit in a track.
As I said in previous posts in here, its more important that the monitors sound true, you don’t want your monitors to make your music sound nice, because then you have something that may sound nice on your speakers, but the track will sound like crap outside your studio.
That is true. Remember, the golden rule: You can’t polish a terd! If you give the engineer a track that the levels are off and the mixdown is all over the place then the master will sound bad. Trust me i know for when I first started out. I was fortunate enough to have a friend who trained me on how to mixdown properly. If you have bad monitors which add color then the mixdown will be off and the engineer will not be able to bring out the master to its fullest.
And we do this because all speakers sound different, as do monitors. A good set of monitors that give you a real true sound… which again is why monitors that make someting sound pretty will really throw you off when you are playing your new tune on various systems.