Indeed they respond great to EQ. Loving my LCD2C with the AutoEQ orataory1990 PEQ preset. But that's because without EQ these are just a pair of broken headphones. It's really beyond me how a company can have such a lousy attitude.
Seems they got a (silent) revision with improved drivers and FR (and slightly less weight?) a few months ago.
Yeah. It's pretty silly to give it a fail in direct comparison to the HD650 when it's biggest problems are easily fixable with EQ while the HD650 will never play as loud and as cleanly as a good LCD-X. (See Audeze Lottery above...)
OTOH, at least stock with no EQ, the LCD-X is probably my least favorite in their lineup and the HD650 is one of very few headphones I find long-term-listenable in stock form, without mods or EQ.
When a headphone cannot be made to sound right no matter what you do because of distortion, breakup, limited headroom, etc then it's definitely a basket case and deserves a rotund "fail".