Is flat frequency response a hoax?

I have seen a number of speaker companies claiming that their design has a ruler flat response. They then proudly display a graph with a flat line as if it's an indication of its superior quality. Poppycock.

Flat response is a myth. Everybody has different hearing so there's no reason to expect that there would be a one size fits all frequency response.
We don't all wear the same sized shoes do we? Everybody has different sized feet. 

There are plenty of flat response speakers that sound horrible. I've heard quite a lot. There are many non ruler flat great sounding speakers too.
Do not be duped by this hogwash. 

If the mixing engineer used a pair of speakers that is 3db down in the mids and top end then he may have boosted that region by a similar amount. Now when the track gets played on a ruler flat speaker it sounds too bright. So as you can see, a flat response is useless.

The company is Rulerflat  speakers but they dont exist anymore... :)
Phase shift vs frequency would also be useful in addition to frequency response.  Impedance vs frequency might also suggest what is happening with the phase.  Two speakers might have identical flat response vs frequency, but sound very different because of phase shifts (different harmonics summing).  Still, all measurements are useful.
"Can anyone provide the name of a speaker company that claims ‘ruler-flat’ frequency response?"

Neumann studio monitors come to mind. See data for the KH-420:
but sound very different because of phase shifts (different harmonics summing). Still, all measurements are useful.
poppycock. if different harmonics are summing they will show up on the frequency response. 
And, golden ears strikes again...

Have you let the adults in the room know that you are playing on their computer?

If they ask what you're doing, just tell them you are trying to inform a highly knowledgable community the correct way to think about speakers, and, how they have been wrong in their pursuits through the entirety of their decades long journey. 

Remember, a hobby is supposed to be a journey, not a destination. 

You only care about the destination, apparently one that you, and only you seem to be able to fully appreciate.

Betcha those earbuds go mighty loud, huh?