The problem is
1. it is hard to get a flat sound in hardware (equalizers can address this)
2. it is nigh impossible to measure the response *at the eardrum* (without measurements, you are equalizing blind; the best measurements you may see are those made inside of a dummy head costing thousands of dollars, that try to mimick the acoustics of the innards of a human ear)
3. you DON'T want a flat frequency response *at the eardrum*, because music is by and large recorded for and mixed for playback on loudspeakers, so headphones need to simulate the frequency response of loudspeakers. While loudspeakers sound near their best when equalized flat (even this has its caveats), sound at different frequencies are attenuated to different degrees on their way from a typically positioned loudspeaker to the eardrum. This is called the "Head-Related Transfer Function" and is different for everybody.
add to that the fact that
4. people's preferences for musical signatures are all over the place; even though pros mix on standardised equipment and theoretically music should sound best when your equipment produces similar sounds to their pro equipment, people's actual preferences are all over the map; people can and do want all their music coloured the way they want it.
--and you have a situation where the ideal of flat frequency response for everybody is simply FUBAR'ed. Manufacturers are kind of stuck throwing phones with different sound characteristics all over the place and see what sticks. No matter how off the beaten track of "ideal" (for the average ear) a pair of headphones' FR may be,
i) some people will find the coloration to their liking
ii) there will almost surely be someone out there whose head / ear / ear canal is shaped so strangely that his / her HRTF matches the whacked-out FR of the headphone and it will almost actually be "ideal" for him / her.
There remains other aspects of sound for which there are more objective ideals (but are harder to measure), such as transient response and freedom from harmonic distortion and resonances. High budget earphones will usually be better in these regards and should sound better than low-budget earphones once the FR has been tweaked to your liking using EQ (which I see you have no qualms about).
In conclusion, yes equalizers can be helpful, but getting them to actually help you is much more complicated than finding some non-existent frequency response chart off the net and cancelling it out on your equalizer.
A scheme that might work is here
and my addendum to it
But it doesn't really work on your beloved Mac