I mean in Aligned, he was always the Thirteen. He was facing the Vector Prime thing where Vector was the Leader of the Autobots, but then his memory restored. Optimus joined back I believe in RID 2015 which then he was one of the Thirteen. Now I can understand why Mark had to go with Convenant roster for AOTP since they had to fit Optimus Prime in the line or smth
The Arisen is like the wielder of the Matrix in most continuities. Most people though IDW Optimus was the True Arisen, but all that shit was a hyperbole.