Please provide a citation that the vast majority of people throughout recorded human history have been literal slaves.
Balog, I'm really not sure what you see as controversial about that claim. Between serfdom, peasantry, debt-bondage, indentured servitude, conscription, and chattel slavery, most people were enslaved either by a central government directly or by a ruling elite.
Do you need me to show you that most people fell under those categories throughout history as opposed to being Lords, Kings, etc.? Or that being (for instance) a serf is being a slave? I'd be happy to address either one, I'm just not sure what exactly you need spelled out for you.