How the airline, regulator, etc. etc. provides this is for them. And it would appear, they failed badly in this instance.
I have seen nothing to say they did fail badly here? Not saying they did not, but no hard evidence to date.
Pilots would need to be completely honest
There are indications this was the aspect that failed.
There are accounts that the pilot had in the past, "suicidal thoughts/tendencies(?)". I will leave experts to decide if this form is suicide is always a risk, or a particular form? And whether anybody with such thoughts should be permanently barred from flying. Obvious problems with that discussed above.
However, I would add pilots (and Cabin Crew) do commit suicide - no idea of % compared to the rest of the population? However, if any previous history of suicidal thoughts were a bar to a Class 1, then surely every pilot suicide - even well away from work - would merit a high level inquiry as to why they were holding a Class 1?
There's a very big can of worms out there, and I'd rather leave it to the experts to interpret and recommend.