I made an analysis of both women in a relative power position in Gilead and how they navigate it in complete opposite way.
Serena Joy gets her power through her proximity to men. Pre Gilead she built her identity on being a public intellectual figure and a wife tied to male leadership (even if let's be real she was wearing the pants in that marriage to Fred)
She always believed she deserves influence because she helped create Gilead. The whole time she keeps trying to negotiate, persuade, and reclaim status, going as far as betraying other women (June). She thinks she can win and regain control within the system she built. Even after repeated punishment, she keeps trying to get closer to power and matter/be recognized on Gilead’s terms.
Aunt Lydia exerts her power through thr control of other women. Unlike the wives, she has no access to male power structures outside of assignment and checking on handmaids and later in matching young wives with commanders. So she built her authority by owning her role within the female hierarchy and accepts the system but learns how to bend it quietly. She never tries to win approval and instead focuses on what is in her control.
The key difference is how both these women view themselves in the power dynamic. Serena thinks she should have more power than this whille Lydia (eventually) realizes and accepts the power available to her and thinks " How do I use it to my advantage?"
Lydia by the time of The Testaments has become patient, strategic and subversive which makes sense because she’s already accepted her limitations and stops expecting fairness which leads her to playing a long game.
On the other hand Serena always struggles and never fully adapts because:she can’t let go of her past identity and her expectation of equality (or superiority) hence why she keeps trying to regain control and reshape Gilead to fit her. And Gilead keeps punishing her for it.
The irony? Serena helped create the ideology but Lydia mastered how to survive inside it. So over time their trajectory switch, Serena becomes increasingly unstable and reactive while Lydia becomes controlled and calculating
They’re mirror images in a way. No matter how she keeps getting put back in her place, until the very end, Serena keeps seeing Gilead as a philosophical moral idea of what society should that is flawed but was meant to be fair (to its creator) and righteous while Lydia quickly understood that it was hypocritical and power driven (vs moral driven). The first wrote the idea, the other mastered it.