More redemption arcs should work with "going native", as they call it in the cop films.
Every other film (or game or book or …) about a deep cover infiltration is concerned with that. An agent, embedded in a criminal organisation for months or years, acting as one of them 24/7, begins to lose sight of their own identity, their job as a cop, becomes attached to their fellow criminals, and eventually betrays the police and genuinely becomes a mobster.
And more redemption arcs for villains (yes this is mostly fanfiction-relevant) should play with that. The villain, captured or defeated or whatever, pretends to reform, thinking "I'll just wait till those pesky heroes are convinced and leave me alone", and he spends so much time pretending he starts to lose sight of his "be evil at the first opportunity" plan and forms friendships with people he was only pretending to be friends with, etc. etc.
