Some overlooked gems:
Bokutachi ga Yarimashita
Eden - It's an Endless World!
Those really deflated me for while.
I'd also consider Promised Neverland, but only because of the squandered potential of the series (both anime and manga).
so why are you focusing so much on slavery if there are many worse things without a content warning. seems to me you just wanna virtue signal on a relevant twitter topic
it's like fast food, really easy to consume and somewhat entertaining. also there's that entire power fantasy thing going on that many people just love.