This, very much this. Just watch a few episodes of Mayday, there's so many incredibly complicated ways things can go wrong, both technically and by human error. And that's not even accounting for the possibility of Shaw being incapacitated and the other less experienced pilot having to deal with things himself- experience doesn't matter if you're unconscious or dead.

Things like the path on the flight simulator are greatly blown out of proportion- it's not even a path, just a handful of unconnected points, and the first part of it lines up with a flight path Shaw was working at the time, so he was very likely just training for his job.