This excerpt from the Battle of the Five Armies EE gives some insight into what went wrong. It seems the team never really recovered from the time Guillermo Del Toro stood down as director and were constantly scrambling to meet production deadlines. When I cast my mind back to the making of The Lord of the Rings they had plenty of time to do reshoots, recast Aragorn, tinker in the editing room to make sure they got everything just right. With The Hobbit, it appears that an exhausted and ailing Peter Jackson was simply doing what they could to put out a finished product on time. As a result, the final product suffered. You can practically see him aging over the course of this video.
I appreciate Weta being candid about the film’s shortcomings. It doesn’t always come together perfectly and I admire their openness in acknowledging that.