I think the real difficulty is that mental health issues are not quantifyable, and cannot be predicted.
If you have, say, a surgical matter, there is a diagnostic stage, a time when you are out of action, and a reasonably good prediction of when you will be back in gear (or that you won't get back, should the matter be serious or a known disqualifier).
But anxiety/depression is another matter. Diagnosis is mostly done by questioning -- there is no standard "test". Predicting the severity, duration, recovery, and possible side effects is somewhat of a black art. Knowing when the patient no longer has the condition is likewise difficult.
Aviation has taken the easy way out, especially the FAA: If you are in treatment, you lose your medical. Period. Can't work.
Now the aviation regulators are faced with the very difficult task to trying to find some way to separate the really disturbed from the large number of those simply stressed or anxious.
I don't know how that can be done. This week's event has aggravated the problem.