The problem with Redemption is that it's an externally-focused oath, trying to redeem others. A conquest paladin having an "am I the baddy" moment and turning into a redemption paladin is like a douchy bully who suddenly finds Jesus then tries to convert people without apologizing for the years of bullying.

D&D needs an Oath of Atonement which would be specifically focused on making up for the shit you did as a previous less-than-moral paladin subclass (mostly conquest, sometimes revenge, occasionally crown or devotion).