Given some of the bad dialogue (e.g., Ares talking about why he likes Depeche Mode), my impression is that Jared Leto used his role as producer to push the production in certain directions that appealed to his personal preferences. I went in wanting to like the movie (I love Tron: Legacy and NIN so I was definitely excited by certain aspects of the movie), but the movie felt too much like a Leto vanity project. So yeah, I think that, in this case, it's fair to blame Leto for the movie's failure, even though, like you say, there were failures across the board, from many people involved.