Since it was the LAND of Shara where Demandred took control of them. Many had speculated that was why we'd never seen him, and that was a great way to convince them otherwise, but it was also deceptive.

As for Hopper and Perrin merging, I would like to see a cite on that before I believe it happened, since there is no reason to think it did (the DO merged Luc and Isam; who did it with Perrin and Hopper?) We never see Perrin manifest a dual personality like Slayer does. Regardless, I would not consider that much improvement since it would permanently reduce Hopper to an extension of Perrin.