Valid.
I'm not sure what I'd do in the actual situation tbh. But I'd consider treating her as an indentured servant (with rights) til I free her. Financially, it'd be difficult to just buy slaves and free them. It's more sustainable/repeatable to buy a slave, work something out with them in terms of tasks, make money, free them after a certain point, and then repeat with more slaves.
But facing an actual person who has been enslaved... I'm not sure I'd be able to just... not free them.
I mean, I don't think characters, on a narrative level, should necessarily do the good and moral thing, mind you. Nor necessarily from a realism standpoint, I'd say that most modern persons, if reborn in a position of prestige in a world with slavery, they probably aren't going to upend the social order. Maybe not engage in the worse sort of abuse, but otherwise just accepting their new society, sure.
The issue is some character doing this shit and then patting themselves on the back (and the narrative going along with it). Hell, I'd even accept the patting on the back if not immediately freeing her was part of a greater plan and all that. But nah, he thinks he can ignore the whole "having her magically bound to him" by just saying some words about treating her like an employee, apparently so he can feel morally superior.