I disagree. He tackles difficult movies and makes okay to good movies. He took over The Hobbit when another director left. It would be very difficult to make that movie with what he was handed. He doesn't make great movies but he does make average ones which nowadays is an accomplishment.
The Lord of the Rings was a challenge for any filmmaker. Difficult material to translate to the screen (maybe impossible without CGI). The liberties with the Aragorn-Arwen angle I think were more to appeal to a broader audience.
Jackson was a natural to take over for "The Hobbit" based on his work with LOTR.
His choices in other material I agree are somewhat questionable. This latest IMHO is to toy with the Steampunk genre (another difficult bit of material to make a film successful).