6. Criticism from training captains would have been very difficult for him. Much more than for an easy going FO.
Crossing climb
I would go with your view as of his possible character as someone interspersed with moments of explosive anger and then deep depression perfectionists who cannot take criticism but in certain company have to restrain themselves from venting that anger and Criticism.
The clue was in the change of mood when the Captain started the briefing something triggered him.
When the Captain left the cockpit my guess is he started a descent dialling in 100 feet, closed his eyes into a meditative state and allowed the jet to descend to destruction on an unaltered heading. He would have been oblivious to everything and anybody. Maybe that would account for his steady breathing an acceptance and resignation to what he was doing.
Why does a child or young adult who hates school suddenly turn up at the school yard and shoot innocent children in the play ground? its hard to understand the mentality of someone like that
Can you forgive someone like that NO what he did was an attrocious evil act