I probably just missed it, but when you refer to flat frequency response are you referring to the sound level at the listeners position, or say 3 ft from the speaker? If you measure the FR at the listening position, depending on the speaker design, the sound could have rolled off enuf to to ease the FR linearity of a speaker with a flat (+/- 2db) measured a few feet in front of the speaker. FWIW.
Flat frequency response
I am often surprised by the number of speakers with "gee-whiz bang" technology but can't even get speaker design 101 right. I can see the benefit of avoiding a lot of signal processing but preferences notwithstanding, flat frequency response seems like the logical place to start and then progress from there.
1) Why is it so hard to achieve?
2) Does it matter?
3) Is it reasonable to say when you skip the basics you are only progressing on a flawed foundation.