Anyone who makes a stupid remark like that either: 1) has never heard true hi-fi, 2) can't afford to buy the good stuff, or 3) is a troll.
There is a third possibility, that is, they listened to the headphones and didn't like them. There are plenty of people out there who prefer the LCD2 to the LCD3, and the Hifiman 500 to the HE6, and even the Stax 007 to the Stax 009.
There is a bit of "no true scotsman" fallacy at play here, where unless you recognize the greatness of 2000+ dollar headphones, you must not be a true audiophile. That is simply not true.
Also, the whole "diminishing returns" argument isn't quite right either. There are simply sonic preferences. It's entirely possible that the LCD3 sounds better to your ears than the LCD2, that doesn't imply that the LCD3 produces a better sound commensurate it it's cost objectively, only that for you it may be worth the cost. For some who prefer the LCD2, there are no diminishing returns for the LCD3, it is simply subjectively a worse headphone for their audio experience. For a small portion of the population, there may be a relationship between spending more money and achieving higher audio preference synergy, but I suspect for the majority of people that relationship actually doesn't exist at all.
That said, the statement that all 2000+ headphones must be overrated was clearly a trolling remark, that was better left ignored.