Ah, this seems like comparatively a huge reach to me, and I think it does a massive disservice to compare the enslavement of Black Americans to penal servitude, even given the outsized representation of African Americans in the US penal system.
I would recommend reading The New Jim Crow or watching 13th to better understand the argument and comparison being made.
It's the system as it was designed to be. I am surprised that you haven't heard about the prison loophole before. It even gets a powerful scene in the film 'Gone with the Wind'.
I think your argument pretty much ignores a major portion of American history post civil war through at least the 1960’s.