That's not really true. James was the main writer for most of Busted's songs, particularly their first album. He co wrote with other people but he was the main driving force behind Busted. Tom credits James as being the person who taught him how to craft a song. Tom co-wrote a few songs on the second Busted album and James was very involved with the writing of McFly's first album.
How is it not true? I didn't say James wasn't. Its a well known fact that he co-wrote some of the most known Busted songs with Tom. Definitely more than a few (and still writes with Tom from time to time to this day). Tom said they would come up with themes and write around that (eg air hostess, weddings etc) and that he learned about song structures through writing with James. He has shown notebooks where him and James wrote a busted song, then mcfly, then busted etc, so they would work on songs for one band then the other back to back. He then applied the same method to McFly when he would write without James. The first song he wrote with Danny was about a hotel and stuck to the themed song style that he had done with James