Board Thread:General Discussion/@comment-2601:603:4F00:C360:84C3:164:CC2E:30E1-20200128221549/@comment-26397825-20200130122515

Monty literally stated it himself in either a 2013 or 2014 panel. If you'll wait a few hours, Chishio will come online and I'll grab a timestamped link to a video where he says it outright. But his words were "all three of us", with emphasis on three, and he was talking about how RWBY was written by the three of them together, not just himself alone.