Following just the book with added white council stuff would still make it feel like Act1 and I bet general audiences wouldn’t accept it very well. There wouldn’t be anything in the film that comes full circle or any kind of proper resolution. Thorin’s showdown with Azog and Bilbo saving his life were invented material but it worked to give the film some kind of arc. I don’t think Bilbo just finding the ring then giving a nice speech to the company about being willing to help the dwarves reclaim their homeland would be enough to end part 1 satisfactorily. The whole film would just be a series of adventures with a sudden “to be continued” type ending with no arc whatsoever to make the film stand on its own.