I saw some people pissed by Agatha not getting a redemption arc at the end of the series, but the real reason is: she shouldn't get one.
She killed so many witches and did terrible things and nothing is going to change that at the end of the day.
I think what they gave us is so much stronger, you see how she’s filled with trauma and can't make herself trust anyone besides herself and her son.
She doesn’t kill witches, because she feels like. She’s a succumbs, she needs the energy in order to survive and that’s something her mother could never understand.
After she figured out how to control her powers I’m sure she could have joined a coven and she’d receive help from them.
But who would trust a kind of witch who has a defense as an attack? And how could Agatha trust anyone after her own coven and mother tried to kill her?
Redemption arcs are more times than not extremely forced, people’s actions shouldn’t be forgiven by a single action. They made us understand Agatha as a whole character, with flaws, traumas and depth and know that, ultimately, her life lead her into doing terrible things, that have no excuse.