The claim that any F/O is "fully trained" has zilch to do with situation. The captain, too is presumably "fully trained".
I totally agree with your post.
I'd like to add a small comment to that if I may:
When "fully trained" pilots sit at the sim they have to pay attention to what they're doing even if it's just a uneventful flight from A to B, because they're being watched (and evaluated) at that period of time, and I suspect that is the main reason for not having such simple malfunctions like a LH RADALT reproduced in the sim, because only a blindfolded pilot would have missed it and it would be regarded as pure waste of sim time.
When doing business as usual they don't have that "eye over the shoulder" so some just might relax a bit their attention to detail.
Wasn't it Epicurus who has said "Do every thing like someone is contemplating you"?
GD&L