I have not read any books by Sloan, but I have read Toole's, and it seems that there is a general preference for a gently tipped-down frequency reponse. I prefer such a 'house curve' myself. It's less "accurate" in the strictest sense, but more pleasing to me, without a doubt. I do appreciate a speaker design that provides flat on axis and smooth off axis response, for sure, it's the best baseline to work from. But then I apply a curve that "sounds nice", because to me, that
is the goal.
Has anyone linked the home theater shack article on
house curves? Stalker, you may find it interesting, as it touches on many of things you seem concerned with and may help your understanding. If you want to go deeper, get a copy of Toole's book.