Akira Toriyama is listed as writer but ...
he was just the creator. The 2.5 rating is justified! From Imdb.
Writers: Ben Ramsey Akira Toriyama
Trivia: "Dragon Ball" creator Akira Toriyama was initially supportive of the announcement of a live action adaptation and asked fans to treat the film as a different interpretation of his work, but after watching the film he was so horrified at this adaptation of his work that he decided to revive the series with the animated film Dragon Ball Z: Battle of Gods (2013). He later revealed that he wasn't allowed to have any creative input on the film and all of his suggestions were rejected.