One thing that makes redemption arc's so much more real and realistic is that they aren't a straight line. Sometimes, people will backtrack and regress. Zuko betrayed the Avatar Gang and Iroh, before actually redeeming in Book 3. Vegeta had his Majin Vegeta arc before sacrificing himself to stop Buu and redeeming in Super. A-Train betrayed Supersonic but after his brother got crippled and he was called out by Ashley, then he finally committed to becoming a real hero.

I like in season 2 we see on two occassions Sera sliding back towards her old ways, but only because of Emily both times. When she transforms at Vox's rally, notice its only AFTER she sees the sinners are upsetting Emily. In the finale, seeing Emily get hurt makes her fall back to making choices from fear, even after "Live to Live". However, while season 1!Sera would've immediately sent the army down, here she learns to trust Sir Pentious and refrains from doing so.

This is made even better because season 1 makes it clear that Emily is a large part of why Sera approved the exterminations in the first place, out of a desire to protect her and the rest of Heaven. And throughout season 2, we see how Emily is a large factor in why Sera's redeeming herself, which is even explicitly pointed by Lute when she says, "You're infecting your sister with your weaknes". Emily truly is her older sister's morality chain.

I absolutely love the fact that both times we see Sera regressing, its because of Emily