I have argued throughout this blog (eg. see previous post) that psychiatry should not reify psychiatric disorder. Mohammed does acknowledge that some psychiatrists do not think the hypostatic abstraction is central to their work. He accepts that the clinical encounter can provide understanding and have therapeutic aims without such an assumption, but falls short of wanting to "rethink the entirety of mental health practice".
As I've said before (eg. see previous post), our modern concept of illness only really goes back to the mid-nineteenth century. Understanding illness in terms of underlying physical pathology does make disease a thing that people have (in Mohammed's terms). The trouble is that psychiatry never really fitted with this development of the anatomoclinical method, which related clinical symptoms and signs to underlying pathology. Most mental illness (apart from organic illness) is functional, in the sense that there is no underlying pathology in the brain (see eg. another previous post).
This situation was why Engel proposed the biopsychosocial model (see eg. previous post). Medicine needs to be person-centred (see eg. another previous post) and this is more obviously the case in psychiatry where there is no physical illness. I'm not suggesting taking the challenge of mad activism as far as abolishing the notion of mental disorder (see eg. yet another previous post) but I would encourage Mohammed to take further his analysis of the critical challenge to the biomedical model of psychiatry. Despite what he seems to think, psychiatry does not need to accept the hypostatic abstraction to be a medical speciality (see eg. previous post).