GEP, let's not get our wires crossed; I agree totally with your key points, namely, the degree of risk. It is absolutely safer to land and swap over (because we're all much better (hopefully!) and have received more training in landing an aeroplane than changing seats in flight).
A lot also depends on the aircraft! Try changing around in a Mooney
It is better to land pull off the runway and changeover there.
I have changed seats in mid flight in bigger faster aircraft where the changeover is simple but it does take a few minutes to get into gear and change from a passeneger metality to a pilot one.
Seeing an array of guages with frequencies you have not loaded, course indicators you have not set can make things very confusing for maybe even up to 10 15 minutes and even can upset your flow and performance for the remainder of the flight.
I can understand that in advanced training in expensive machinery one student pilot monitors from the back and changes over midflight to take over the second portion but that should be well briefed before and the second pilot should be monitoring every move from the back so that when the changeover occurs the confusion element is kep to a minimum.
Pace