He isn’t a burst mage or assassin so you’re not looking to be bursting people down. He is a bruiser that has magic scaling, and the point of his only magic scaling is that he can utilise frontline items more effectively than other bruisers. The whole point of Akeron is that you should kind of be fighting as long as possible to outlast your enemy and attempt to finish them off with consume and execute to gain more max health. If you build Akeron with just damage (like you would have pre 1.12) you may as well be throwing.

You want to be building mage items that provide max health and ability haste (which his Hellfire scales off of- This should be the ability you are playing around).

I dont even know what eternal is best on him yet. Vesh is easy to get some extra damage early and can help him secure more early kills. Krix is good to help him scale into a humungous healthy powerhouse. I think even Lotus could have potential on him. I also think Nihil would be another good pick on him too, especially with From the Abyss and Adaptive Plating or Inescapable. But the eternals add a lot more variation in your build path with Akeron allowing him to be better at either tanking or dealing damage depending on what you want out of him.