Re: John Harrison was more interesting than (SPOILER)
It does feel like somewhere in the process they went from Harrison to the Khan/Harrison villain. Maybe as late as shooting the film.
I think the Harrison facade could have been done away with completely and wouldn't have changed the movie much, as well.
"I had no idea you were so... formidable. " - Anan 7 to James T. Kirk, A Taste of Armageddon