I agree in one way, I think sometimes a diagnosis of mental illness is used so deeper investigation isn't warranted. I certainly think that's the case for me, I have suffered with depression, and been diagnosed with it. However I also have physical symptoms that aren't explained away by depression or helped by it's treatment. When having blood tests I'm always 'borderline' no treatment required for Thyroid function. But I'm not a text book, just because the average says at the borderline level I don't need treatment, it doesn't mean that I don't have the physical symptoms, or that treatment wouldn't be effective. It's not even tried though. So I'm diagnosed with depression, because physically on paper I'm 'fine', and the physical symptoms persist. Because anti depressants don't help them. It's like banging your head against a brick wall.
I'm starting to face the same now I'm getting to peri menopause. Blood test (that even they tell you aren't accurate!) say hormone levels are normal, so that's that, too young for hrt, must be depressed and this time have anxiety too. Here's some more anti depressants. Off you pop. Want some talking therapy? Sick note because you're not coping?
No, no I don't, I want the physical symptoms that living with makes me unhappy addressed and then maybe I won't be depressed! Sore joints, crushing fatigue, constant itching, insomnia all things that sap the life out of you and yes, make you depressed when you're trying to live with them. Other signs are present, longer between periods, skipping them, then flooding etc. But no, you've got depression and anxiety. Off you go. Just because I've had depression doesn't mean I can't suffer with physical illness, or a very normal part of aging as a woman that brings with it some problems that can be addressed.
On the other hand, mental health services have been cut to practically non existent, seems like they're trying to change the narrative from 'Not enough mental health services' to 'too many mental illnesses being diagnosed'.
In both cases a lack of diagnosis isn't going to stop any illness being there.