Powers as allegories for trauma responses and how they relate to the character arc is so beautiful
El's are motivated by anger demonstrating the fact that she has learned she has every right to blame and hold responsible her abuser for abusing and not herself, that being angry is completely justified and she will no longer be gaslit into thinking she caused her own suffering, and in that is able to be angry at her abuser and not herself. There's a quote I love: "anger is a part of you that loves you". Because it is telling you when you are being mistreated, it is telling you that you deserve better.
Will's are motivated by love and peace demonstrating the intense strength required to remain gentle in the face of violence, to not become your abuser no matter how much they try to make you into them. Lonnie wanting him to be more "masculine", even Vecna wanting to "use" him for a better means. The strength in the refusal to let your abusers goad anger out of you in an attempt to turn you into them.
Brenner tried to convince El to not be angry with him because her abuse was her own fault. "Now you are angry with yourself and you are taking your anger out on me". But she refuses.
Lonnie and Vecna tried to goad Will into BECOMING angry, violent, because those are the traits they valued and were trying to abuse him into being. "Some minds simply do not belong in this world, they belong in mine." But he refuses.
She refuses to be blamed and harnesses her anger, validating it as rightful.
He refuses to be goaded and harnesses his love, refusing to turn into them.