To be blunt, I just think that Rowling needed a very honest editor who would tell her when something was incoherent or illogical - and wouldn't hold back with the red pen. A great deal of the stuff I have problems with: the failure to follow through on the four element/balance thing of the four houses, Ginny the fembot, etc - would have been jumped on, ordinarily. I wonder whether the sheer success of the novels meant that critique became a no-no?

I think your idea is cleverer than what Rowling was probably going for. :)