Oki... I went away and did a lot of thinking about it. Here's what I see.
a) Ahlaric pulls a Mace Windu death: He appears in the scene - poof dead - story goes on as if he's unimportant
b) As I note in my review, he gets a free pass-- kind of dying quickly after a night of partying.
For point (A): much of Windu's issues is the disconnect between his actions and his fate. Really, his game-changing actions (slaying Janga Fett) should have been daisy-chained to his passing. By not doing so, you have this odd character doing weird random things then dies randomly, and is forgotten (and unavenged - who would want to avenge such a random?)
Consider Windu: Helps Anakin (child) survive. Leads the Jedi against impossible odds at the coliseum. Slays galaxy's most feared bounty hunter-- the one they clone super soldiers from. Challenges the emperor personally. Dies relatively easily falling out a window.
Consider Ahlaric: Man breaks the empire. Orders the extinction of a planet. Carries it out. Orders a genocide. Watches his people crying for help and laughs in their faces (and dances). Dies quickly while sleeping off a drug-induced haze.
If you can see the parallel, here are some related thoughts:
1) Ahlaric has no time to regret his actions. Sleep - pain - dead.
2) The people he hurt do not return the favour. The events he set in motion do not cause him any distress or fear or worry.
3) Even the servant he abused doesn't technically get revenge since he's possessed.
4) He should do something directly evil in book ii (eg not evil by neglect but actual evil). Imagine sitting down to watch the latest Batman, and in the first major villain appearance, Batman shoots him in the head and says "that was for what you did the other movie"
5) (Related to #4) the slaying of the villain should be by a protagonist. It is okay if that protagonist is then slain by Omhara. Be prepared for people to love that protagonist and really hate Omhara.
Note 5 is a classic wrestling concept "Put One over". Heels turn on heels all the time, but they don't defeat each other (except heel-to-face turn). Heels turning on each other allows faces to take wins. Heels love beating up faces once the face thinks he's won