Carla does not contest Mark’s understanding of any historical events. She argues that Mark’s suggestion would generate biased versions of history, not that Mark already believes in a biased version of history.

Nothing in Carla's argument suggests that she questions whether one person can understand another person's feelings — nor does she claim that Mark makes this presupposition. Her argument is about what would happen if historians decided to focus on certain perspectives over others.

This is correct. Carla points out that Mark's suggestion requires selecting whose perspective is considered valid, and argues that this would lead to a biased account of history.

Mark only gives suggestions for how historians should approach their work. He never comments on, let alone "deplores," any kind of historical writing that already exists — nor does Clara claim he does, or does so inaccurately.

Clara doesn't say anything about Mark's profession or his self-interest. She focuses on an undesirable consequence of Mark's suggestion, not on any of his motives.