Depression can only be treated as a symptom. It is a phenomena, a “mere idea”.
A good way to think of it, is depression is depression - NOT neccessarily low dopamine levels, etc.
Depression is also tricky to easily pin down for a simple answer- there are many forms of it (bipoler, cyclothimia, etc) - many have very real signs and symptoms of their own (of which quite a few are physical). In many cases depression may be more aptly looked at as a syndrome or disorder than a disease - but that is beside the point (this should be uncontroversial). The point is that the “medical model” by itself tends to be insuffucient for many of these psychological ailments (which are very real)- though pharmacology can indeed help, in many cases, particularly mixed with therapy.
People just have a tenedcy, especially in the popular mindset, but also within certian schools of psych thinking - to turn a method into a mindset. This is bad and not good for patient care.