Trauma -- especially if it happens over time, as in PDSD -- causes biological changes that are difficult or impossible to reverse. While the symptoms may closely resemble those of mental illness, they aren't. It's a mental injury. There's a world of difference between being unable to do something because your body/mind built itself wrong or went awry due to internal flaws, vs. getting hit by a truck. As the article points out, the treatments differ enough that what helps pure ADHD may be ineffective or actively counterproductive for PTSD.
Why are the numbers going up? Well, if they're right about the stacking and/or misdiagnosis, it's partly because poverty is going up. Stress and low resources can do a great deal of damage. Of course people wind up with problems. It's worse in children, who have minimal control over their lives or coping skills to buffer the damage. So if it's not correctly identified, it basically ruins their life.
This really got me thinking about Shiv, and for that matter, a lot of my other supervillains. Most of them come from a crummy background, especially poor or working class. Most of them have been abused and/or neglected, often starting from a very early age. You can see why so many minions can be "bought" for three hots and a cot, why the Marionettes have such a strong Family structure, why Kraken seeks out troubled youth to recruit and offers them an honestly terrific benefits package. It's also how Shiv wound up in such a mess. His trauma started so early, he never had a chance to develop the usual skills of self-regulation, and he expressed his damage in some very disturbing ways. So very quickly he went from being considered a victim to a problem. But it's not a mental illness. It's scar tissue. The symptoms are the same, but the source is different, and none of it is going to get any better without going back and repairing as much of the earlier damage as possible. Create healthy connections. Teach coping skills. Understand that when he acts out, it's not because he's a bad person, but because his life fucking hurts and he can't help flinching. And with that in mind, look for ways to prevent him from harming himself or anyone else while he's skilling up. Or at least minimize it, since he's not actually willing to let go of either the sadomasochism or the criminal profession.