@BATHALA_ First off.... nice profile pic.
Secondly.... yeah ever notice how most summoned heroes have little to no understanding of economics?
Granted I don't like this kind of slavery either, it breeds hatred and resentment. The slaves are treated worse than livestock and aren't afforded basic quality of life measures that'd make them better workers, and more important to the slave merchant, better products.
A happy slave is a productive slave, content with their lot and unlikely to cause/join in a massive uprising should the opportunity occur.
Poor sods probably don't even have the option and ability to buy back their own freedom from their labors either. ... I really don't get why the bondage price isn't a more common thing in fiction tbh. It's all "slaves are less than animals" or "slaves are subhuman furniture"....
Hope makes a man work harder than anything else, the hope of someday being able to be free by your own labor would massively increase productivity across the board... save for criminal slaves. Mass murderers, rapists, child molesters and.... I can't think of a fourth crime worth sending someone to work till they die in a mine for actually.... well a mine or other hazardous and labor intensive activity.
He's probably going to just abolish it entirely and give the slaves their freedom, land and citizenship anyway because he's just that kinda man and there's only so much of this shit you can stomach as a general rule anyway.