You can't separate the concept of abuse from power. Put another way, the concept of power is larger than the cycle of abuse, but it will always include the cycle of abuse.
Astarion does tell you who he is depending on the choices you make. He also may not. He's certainly very open about his pursuit when it would be easier to lie and make himself seem easy to protect. There is a lot of tentative honesty. Tentative trust, conditional trust, placed on the belief that he is in control. Astarion is a very certain type of person. The type that cannot trust nor feel safe when not in control. That's why he manipulates in relationships as well, and sees them as a *resource*. You are a resource to him. The growth people see in him is the return of the capacity for some other emotions, sociopathic as that may sound.
Food for thought: when people try to write an evil character, they tend to to mean selfish. Astarion making an unselfish decision by sparing the spawn is by this logic the good route. It's not redemption and it's not change. It's about even having the *capacity* to be unselfish, and therefore be good, which before this point was not clear. I'm aware this is not very satisfying. I've had my own gripes with the spawn ending.
