Idea for Isekai fantasy plot with a dark twist

The general idea is Human women agrees to be an Isekai Hero in another world. But when she gets there she realizes she's been tricked. This world already has millions of would be "heroes" who were all enslaved by the local beasts/ evil empire. The entire economy is based on the mass of free labor brought about by human women entering the world with no way to return home. Because these women enter the world with the mission of destroying the current government, they are condemned to a lifetime of service as a more humane alternative to death.

Ive been attached to this idea for a very long time but not sure how to expand on it, or how to use it in a narrative. The story is just an Isekai fantasy turned on its head but I don't read Isekai so if anyone who does could tell me how this could work?

I might expand on the slave catching, training, and distribution pipeline. I was mainly interested in the idea of "Fantasy hero on an epic adventure " being industrialized in the most evil way possible + self indulgence in dark kinks (slavery, degredation, domestic service, etc. )

Note: no sex slaves. Slaves still get used that way but its never someone's main job. I kinda hate the idea of a slave only ever being used for sex.

Thoughts?