But that contradicts Padme’s line about there still being good in him (Anakin)
No, I’m positing this from an entirely RoTJ 1983 perspective. The prequels would then have been written with this in mind. You’d have a big emotional scene in ep 3 where a dying Padme makes Obi Wan swear that he’ll preserve her version of things for Luke’s sake - thereby justifying Obi’s adherence to the narrative. It wouldn’t have to be throwing Padme under the bus per se. There could be subtle dialogue (in both RoTJ and/or the prequels) indicating that Obi Wan more or less agrees with Padme’s perspective in terms of separating Anakin and Vader as entities.