Imo 'depression' should be considered a category of symptoms, but not a diagnosis. I mean, it's like 'fever' - a fever can have 1000s of different causes, it's ok to try paracetamol first, but if it keeps happening then investigate more. Ditto for depression: try an SSRI first or for some relief in the meantime, but there are so many different causes for depression (I wrote a list of 20+ I know of), many not originally psychological, trying to treat them all as the same thing often doesn't work.