They actually are more complicated than social constructs, I mean people with mental disorders often suffer very real, debilitating symptoms...its not like the term depression just gets randomly applied to people for instance one gets the diagnoses from suffering very real depression symtpoms. Also whilst criteria can be altered/changed and names of disorders can change its not as if every disorder is constantly being drastically changed into something else. For instance what is considered anxiety symptoms now was considered anxiety symptoms 10 years ago to.