It seems almost like the cure for depression is being depicted as "just think happy thoughts." Which, yeah, that doesn't work.
But I think that's just somewhat clumsy phrasing. If you look at what's really going on, you can see it's not about Polyanna-ing your way out of severe mental health problems. It's more that positive thinking is something that has to be nurtured. Koo'bur says it best when he tells Mag, "It will be the hardest thing you'll ever do," and while the battle is endless, "it's one worth fighting."