Historia's place is still unclear to me. She's not against the genocide, but doesn't want the memories of it to feel guilt over? Am I understanding that right?
More or less.

She understands that Eren's plan is the most rational one if one was to prioritise Pradise Island's prosperity above all else, but she won't be able to get over her personal guilt. Eren was willing to wipe that guilt from her.

I understand Eren's side of things.

If one was to ensure no further Eldians get into a cycle of hating each other due to the titan issue, and one was to prioritize Paradise Island's welbeing above all else, genocide is an actionable plan.