In an odd way, Khan is a tonic for both Kirks. That does kind of make him Kirk's Joker. Kirk needed Khan both times. Both times he was reborn into the full hero he is (maybe even literally in STID). I kind of like that.
That's an outstanding way to look at it, and if people cannot see that Abrams put a lot of thought and depth
into this film they are simply blind to it or more likely just simply don't like Abrams style and will search for anything to complain about.