Yes we do.. you just aren't paying attention. He is denathrius brother, he is the leader of the nathrazeim who have been playing everyone since basically the beginning of time. He had his nathrazeim steal and place frostmourne and the helm of domination in azeroth so he could have the lich king user him in, but when we defeated the lk and bolvar put the crown on he was fighting back the jailers commands with the strength given to him by being cleansed by alextrasza's breath. So he had to go another route and started working through the death gods like hela and muezahla in order to get sylvannas into a place of power so she could help usher him through. As someone said everything so far is going according to his plans. Sylvannas is really the only reason anduin isn't Arthas 2.0 yet.