I'm not aware of impostor syndrome being considered anywhere on the same level as actually diagnosed depression/ADHD by physicians, nor of it being considered for addition into the DSM, slow and bureaucratic as it may be.

The variety I'm referring to is the one that comes from people like the one I originally responded to, who, by all accounts, is a successful functioning member of society. So, yeah, I think it's fair to say "claiming impostor syndrome is just describing a normal feeling" in contexts where the person is clearly not overwhelmed to the point of dysfunction.

Even if there is such a thing as actually crippling impostor syndrome, that's not what I see being brought up in these kinds of discussions.