I don't have a problem with that, in theory.
Most of the stuff with Dol Guldur and such is actually in the Tolkien mythos, primarily in the appendices to LOTR.
The problem is that The Hobbit is a children's story. It's told from the perspective of a funny little person, quite unsophisticated. For most of the story he doesn't have a clue about the larger picture of what's going on around him.
What PJ has attempted to do is take this small, sweet story and turn it into an epic, with the scope and scale of the LOTR movies, which I thought he in general did quite well.
However, I fell asleep in the most recent Hobbit episode. Too much video game nonsense.
My complaint is not so much that he expanded the story, but that he did a poor job of it.
I haven’t even seen the first Hobbit film - but I really liked LOTR