1) It isn’t always better to have 2 individual (Olympic) events. Focusing on one event can improve your medals chances, examples would be Manaudou, Proud or Armstrong.
2) He has a chance (probability greater than zero) to win a medal in the 200 back, but it is impossible to tell from the outside how big his chance is. So far he hasn’t shown anything to indicate that he could be one of the favorites for a medal. Training for the 200 back might destroy some of his speed, which could hurt him in the 100 back. At least the 200 back schedule doesn’t collide with the 100 back/4 x 100 free/4 x 100 Medley schedule, so it probably wouldn’t hurt too much to give it a try.