I believe I have read that Hogsmeade focuses on the first 4 books, Diagon Alley on the latter 3. I don't think either is supposed to be set at any exact moment. Instead, they are set in a sort of "universal Potter time" that includes all of the best moments and some of the most heroic plots from the books. Thus, Dumbledore is eternally alive at FJ, Mad-Eye Moody is eternally alive aboard the Hogwarts Express, Voldemort and Bellatrix are eternally a threat (but are continually thwarted by Harry, Ron, and Hermione) in EFG, and Ollivander's shop is eternally selling wands in Diagon Alley.
There is no way a dragon can be sitting atop Gringotts at the same moment that Ollivander's is selling wands and Florean Fortescue's is still selling ice cream. Diagon Alley is pretty much shut down and crawling with deatheaters, with the exception of WWW, from the beginning of the 6th book forward. So instead of being set in a particular book, the Wizarding World represents an amalgam of all the best moments in the books and movies, but with particular moments in time (e.g. the trio's escape from Gringotts on a dragon, Harry's wand purchase) brought to life in detail.
And besides, if DC is the main hint that Hogsmeade is set in the 4th book, then replacing it with a Forbidden Forest adventure set in the 3rd book would change that.
The choice between whether it's better to go with canon and recreate specific plots that the guest participates in on a parallel adventure or to create a purely guest-centered adventure is a personal preference. I like both, but I do think employing dramatic moments from the books/movies gives the rides a more authentic sense of drama. Kong is disappointing because if its shortness but also because the storyline consists of nothing more than "there are scary, bad things in the jungle and we must get away from them! Oh look, Kong not so bad after all, yay, we're safe!" Likewise, I think that a Forbidden Forest ride whose plot consists of nothing but "Magical creatures cool! Oh wait, some of them are evil, we're doomed! Nah, it's all good, yay we're safe!" would be a bit disappointing, too.
If you're absolutely opposed to the idea of bringing specific scenes and plot points from the books into the storyline, what other kinds of mission or storyline would you incorporate into the ride? I feel that the "Muggle visitor is invited to ride aboard a magical mode of transportation to get to a place to do a thing, then bad stuff happens" in and of itself is insufficient unless there are specific plot points and characters from the book woven in. How would a Care of Magical Creatures class visit work without incorporating scenes from Prisoner of Azkaban, if they went that way?