wow that's incredible disappointing
i'd like to point out that's not what it means
flat EQ doesn't mean there's no processing, headphones almost never do processing. It means that the drivers reproduce sound without any emphasis on a particular part of the sound. A 50Hz tone is going to have the same real amplitude as a 6KHz tone.
Note that that doesn't mean that to your ears it'll sound like a 50Hz tone is the same as a 6KHz tone, since the ear has different sensitivities to different frequencies. That's why some people prefer a "warmer" sound that has the bass slightly emphasized naturally. An example of those would be the Bose QC15's which I own.