I suppose, what it really does is gives it a name (or I think it’s what it should be.) I cannot really relate this with ADHD, because then in a roundabout way I may be suggesting that being asexual is a “problem”. It’s not. Neither is being homosexual. Or bisexual. These are just terminologies to describe our sexual orientation (and preferences). If someone is using the term “demisexual” as derogative, then it’s really their fault. Instead of “questioning” this term, I think what we ought to do is make it commonplace. When we meet a potential partner, we ought to say Hey, I'm demisexual by the way, just like a bisexual partner-interest may say that, not to suggest they are lacking in some way in their sexual orientation or preference, but just that, that’s who they are.
ADHD on the other hand — is a problem. And misdiagnosis can be an issue, but these two terms should not be compared as they are nowhere near the same, but people’s perception, yes, that must change.
Hope I made sense there, I’m not very good at explaining.