There's all kinds of proof. Staten's original "supercut", the .dat files and the fact that the taken king disc is literally nothing but an activation code for the content, oh AND THE DREADNAUGHT WAS SHOWN IN THE ORIGINAL TRAILERS FOR THE GAME. They didn't just magically come up with it after the fact, it was already planned because the Dreadnaught was where we were supposed to go to rescue Rasputin in Staten's orignal script but then Harold Rayan like the idiot he was didn't like it and had the whole thing canned. So they just repurposed the assets that were already made. Honestly if it wasn't for Nathan Fillion TTK's campaign would have been pretty crappy.