How relatable does a historical character need to be to a modern audience?
With historical fiction, one of the problems is when characters sound like 21st century transplants. (Like when you’re watching a show set in small-town 1950s England, and the protagonists neatly share the viewpoints of a liberal Twitter commentator.)
I understand why writers don’t want to create protagonists who heartily endorse all the common prejudices of their era. But you don’t have to do this in order to write a good piece of historical fiction. You don’t need to go out of your way to make a character (especially a heroic character) deeply bigoted or hateful. You can also write about harsh historic realities without resorting to slurs or lazy stereotypes (for example, you can write a servant as a more well-rounded character and not a caricature with a Cockney accent).
But you don’t need to use characters as a vehicle for preaching certain opinions. Or soothe modern audiences by promising them that they won’t encounter anything truly different in fiction – they’ll see themselves or people just like them wearing historic costumes, like at a Renaissance fair. Reassuringly familiar, even if it’s also more boring and the story loses some truth, becomes flattened.
Why does every character need to be completely relatable anyway? Humans have always been humans, but thoughts, beliefs, and emotional expressions are all shaped by culture and historic period. I can enjoy a story from the 19th century and gain insight from it without needing to pretend that the protagonists would see eye-to-eye with me on everything (or even most things). In many ways, including how they think of words like “honor,” they’re drawing on different conceptions, different interpretations. It’s possible to find some common ground with these characters without pretending at sameness.
As for showing a protagonist’s relative lack of prejudice or greater compassion, it’s best to use actions rather than preachiness. Even subtle actions can convey understanding, humanity, and good-natured humor, and there’s less risk of the character sounding like they time traveled.