I wasn’t equating slavery with capitalism here. I was comparing your reasoning with the reasoning of those who argued for the status quo during times of slavery.
Except that at those times, you could absolutely compare slave economies to non slave economies, and the non slave economies were healthier
It's why during the civil war, the north was so much more powerful than the south
Turns out that if you stifle the potential of half your population, lock them in bondage, and assign a significant portion of the rest to watching them, it's not very efficient. It's better to just pay people, even discarding the abominable immorality of slavery and focusing on just economic efficiencies.