Turns out maybe I was hoping for
1) No slavery
2) Actually named characters with their own, you know, personality.
I think that you're misunderstanding a major aspect of this story - this MC is NOT a good person, and the story is in no way pretending that he is. This isn't an edgy self-insert with some sort of justification to do evil acts, he's not some tragic fallen hero forced by his circumstances - he's a selfish prick exploiting his slaves in order to get paid for doing a noble's dirty work.
He uses slaves because they're available and he has no moral opposition to that. They surely have names but they aren't important because they aren't important to the MC, whose perspective we see this story from most of the time. Also from a simple storytelling perspective it'd be pretty cumbersome and wasteful to list out the names of dozens of slaves that don't serve a narrative purpose beyond how they affect our impression of the MC.
Instead it's the usual slop where all the girls are slaves, because without slaves the average target demographic of this manga can't even imagine getting pussy. And they're mostly noname mobs, with like 1 girl up to this point that has a name.
Also, harem does not mean 200 nofaces girls with for whatever reason are fine with being slavegirls. And the dude fucking a line of girls every night is not even sexy or funny, just retarded.
The reason the usual slop does slaves is because it's extremely easy for a lazy writer to build a relationship where the good-hearted protagonist saves a girl from a life of torture and abuse by being a "good" master, while also still fulfilling the power fantasy of having absolute control over a woman (sexual or otherwise). The slop has the girl believe she's a princess (sometimes literally) being rescued by a handsome prince, and as a result would follow the cardboard cutout MC through anything even if the slavery collar/spell/whatever was removed.
Again, this manga is VERY CLEARLY not doing that. This manga is doing slaves because the MC is an asshole, the noble he's working for is an asshole, and the country as a whole seems to be largely run by assholes. The MC raising slaves out of their poor conditions isn't depicted as being heroic, it's depicted as manipulative and self-serving. The girls may think the MC is their savior, but the MC is simply exploiting those feelings - and the MC fucking a line of girls every night is another way the manga is showing how
HE is a piece of human garbage. The dark elf even remarks that he's no different than one of the evil nobles in that respect, I'm not sure how someone would miss this.
Who could possibly imagine that EXECUTION actually does matter in manga, right?
I'd argue it's not poor execution just because what the author is trying to execute isn't what you think it is.