I don't disagree with you, but it does seem like you're using "do the meds work" as the key criteria of whether its a trait or an illness. But I guess I don't understand why that matters, apart from "how should we socially judge this person?" There are a large number of mental and physical illnesses that can be improved (by the judgement of the patient) by a wide range/combination of meds, actions, choices, etc...

If I have schizophrenia and I treat it without meds and I get better, that doesn't prove you wrong. If I treat it exclusively with meds and get better, that doesn't prove Caplan wrong. Because it doesn't matter to me! What matters is: "by my standards and accounting for the cost of treatment, did I get better?" If you want to say "schizophrenia that you can treat without meds doesn't count" then I am 100% fine with that - but I think you (and Caplan) are fighting over definitions instead of reality.