Until Arthur shows up, I'm still not sold on that he's suddenly evil. He never gave that impression in the previous series, it all ended on a good note there, so if he is acting off then I assume the chaos power he has now must be involved in some way.
That or there's going to be multiple layers of misdirection on this, and that both sides are viewing the other differently or trying to orchestra events, etc. The horsemen bringing ruin could be good or bad depending on the stories being told after all.