I agree. Flying an aeroplane is simple. The difficult but is putting your brain ahead of the aircraft and when things go wrong, remaining ahead of the aircraft, the failure, its repercussions. And then there's the ability/youth trade off. Most FOs are younger than the captain and as a result have faster reflexes. They are also capable of flying the aircraft just as accurately (or even more so) as their colleagues. So getting them to fly when things are going badly makes a great deal of sense.
PM