I dont think its over diagnosed, try getting a bed on a mental health inpatient ward - its very hard, so you end up with people discharged to the community who shouldn’t really be there.
I think what he really means is that too many people are not working due to mental health conditions, i partly agree with that, but i also think our work culture is to blame . Most people i know work crazy hours, with lots of unpaid overtime, even in low paid roles. I left my job due to the impact on my mental health - the pressure, the expectation that i would cover multiple vacant roles - it was just too much. Im not on benefits, but its a loss to the economy that im now working few hours not using my specialist skills.