One difficulty with making comparisons with the past is you have to define which past, whose past.
My MIL who was evacuated as a teen during the war, narrowly escaped death when they missed the boat which was subsequently torpedoed, returned to England as an older teen and sank into depression when unable to connect to her parents was in a rather different situation from her son who was brought up in a stable family situation in the 70's.
(and yes, MIL was medicated, apparently on something very closely resembling heroin)
Plenty of evidence for depression and other MH disorders in the aftermath of WW1 and not only among returning soldiers.
Plenty of mention of valium in the 20's and 30's.
There was some reason why psychiatry was already going strong in the late 19th century: a lot of those practitioners made money treating depression.
There is also a reason why acedia (= depression) is counted as one of the mortal sins in the Middle Ages- and it's not that it's unheard of, any more than they put gluttony or lust on the list because nobody had ever come across those.
In my family there is a clear genetic line of depression going back at least until the early 20th century. But only one figure in the statistics: that of my dd. The rest just had to lean on their families.