Gotta say this was a lame decision. It's a single player only tournament...why ban anything at all? Leave it to the player's discretion as to how easy they want to make it. BP are hardly an item they should consider needing to increase the effort of obtaining, as they are, once again, just a means of training/breeding better 'mons in a legitimate way. So what if the player can use legends to gain said BP faster...its not game breaking even if they use those BPs to make 'mons for use competitively, since they weren't hacked into existence.
Edit: I see that there is a downloadable event for legendaries, so thats at least some consolation.
"All your sweetrolls are belong to me." Video play throughs at - http://www.youtube.com/user/DreadArkive