Hierarchies are a natural thing. Established official, and social, hierarchies define a civilization.
Slavery is about ownership of people. People in charge is about social hierarchy.
How is people in charge, social hierarchy, not about ownership of people?
What is slavery? If owing 100% of someone's labor is slavery, is owning 1% of their labor something different? With people in charge, how are those who do not consent, consenting?
No one owns your labour in the current system but yourself. You sell your labour. Someone will purchase your labour if they have a demand for it. What labour you offer matters.