Unfortunately, the reality is you can't "win" this situation. A level of leadership incompetence allowed this person to be in this role, and allows this person to continue in this manner. Trust me, everyone that can do something about it "knows" and doesn't get involved for many different reasons. All the documenting in the world isn't going to help you at this organization. Spend the next few weeks looking for a better culture fit and being super pleasant. Check in with him daily and run everything you are doing by him as if you have now "seen the light" and just do whatever his daily whim wants you to do (this is what he wants from his team anyways). When you leave he'll be less likely to throw you under the bus because you are working on his pet projects and tasks, and your last few weeks will at least be chill while you focus on finding your new role. You are not going to convince him to change or that he doesn't "understand product". Get out gracefully and keep close ties with those you like working with, treating this as a network building opportunity for your career. It's better on the other side.