No, it’s relatively easy to prove that all forms of slavery, even voluntary ones, are less efficient than simply paying wages. This is because it removes the capacity for future choice. An employee in a low–paying job today can leave for a new opportunity whenever one appears, a slave or an indentured servant cannot. Societies which use slaves or indentured servants will have less economic success over the long term than ones without.

> Also, how does any of this prove that having people travel 4 hours a day is economically productive?

It’s manifestly more productive than being unemployed. It might be a bad enough job that you can barely tolerate it, but that’s better than starvation. An employer whose employees are this close to the edge is taking a very large risk. If any alternative opens up, or if the job conditions get any worse, then they will suffer fatal turnover. They’ll either have to pay higher wages or improve conditions (or both) to survive, or their competitors will do it for them.