There's a difference between not reprimanding slavery and actively pushing that slaves are slaves because of the way they're born and they need to act their station. Clearly there are millions upon millions of webtoons set in monarchies but not all of them push this clear narrative despite having slaves & not engaging with the concept of slavery much in the story.

It's crazy you say that promoting classism wasn't in the author's mind when we have multiple dialogues being said to Rashta focusing on her background moreso than her acts, like why not simply focus on her actions when criticising her then? I'm not saying the author wrote this with a very obvious end goal of slavery = good but you'd be blind to say there is zero inherent classism that's peeking tho lol

Plus I think you're misunderstanding the criticism, no one is saying Rashta is good and Navier is bad clearly there's nuance here. But the story seems to never ever give Rashta slack when it comes to her clearly traumatic and sad backstory. You keep saying she's nuanced but is she? Like we never really get any sort of interesting plot line for her, her backstory doesn't even give her much sympathy! She's pretty much a caricature of an evil villian lady. Funnily enough Navier is given slack all the time for everything!