What he's done is have an arc that parallels Kaladin's, but taking the opposite choice from Kal at major turning points. In order of importance:
Both have a particular lighteyes they hate, and teeter on the edge of being destroyed by the grudge. Kaladin learns to fight the corrupting influence of that hate, where Moash feeds it. Both kill the lighteyes in question, but Kal does so in defense of Dalinar, fulfilling his oaths as a windrunner. His personal beef with Amaram is no longer his motivation. Moash kills the king in a dishonorable way, and solely for his personal gratification.
Both are offered two different shardblades. Kaladin rejects both Blades he is offered, where Moash doesn't hesitate to take either Blade.
Both become a lighteyes through various means. Moash allows this to separate him from Bridge 4, where Kaladin remains connected with his friends.
Both have serious doubts about their position as Elhokar's guards in WoR. Moash abuses his position to aid the assassination attempt, while Kaladin ultimately honors his by saving the king's life.
The two respect each other greatly, even after clashing so many times.
Each has a powerful mentor who is intimately connected to one of the Shards: Dalinar (Honor) for Kal, the Fused (Odium) for Moash.
Each trains a group of outcasts in the spear: Bridge 4 for Kaladin, the group of parshmen for Moash.
Due to Moash now having Jezrien's Honorblade, both of them have access to the same Surges at the present time.
Moash is the Vader to Kaladin's Luke, the dark reflection whose narrative purpose is to show what he could have been. The most hearbreaking (and totally Brandon-ish IMO) conclusion to their arc that I can think of is for Moash to become Odium's champion and for Kaladin, as Honor's champion, to be forced to kill his former friend.
EDIT: Lolme for basically rehashing a conversation that was already happening in the thread. If I would finish reading before responding to somebody, this stuff wouldn't happen