Slavery is almost never preferable to paying a wage when there is an available supply of labor. But almost everywhere slavery (or forms of it like serfdom) have been in heavy usage there were labor shortages.
The assumption is that you can just always replace slaves with minimally paid persons because there are so many people desperate for a minimal wage that you can just pull them out of a hat. That just isn’t the case. The Roman Empire needed slaves working in agriculture for example because the Romans demanded a large assortment of luxury agricultural products beyond just baseline subsistence.
Many people who lived under Roman rule lived in the same semi-autonomous tribes/communities as they always had. They had ways to basically feed and clothe themselves despite not having much capital. So it is highly unlikely they’d quit doing whatever it was they were doing to work for minimal wages in some far off province growing grains to feed the Roman war machine.
The New World was no different. If a huge portion of the natives hadn’t died off due to disease, they still would have little incentive to work for a pauper’s wages. These people got along fine doing their own small scale agriculture, hunting, fishing, trapping etc. What reason would they have to abandon all that to work for a minimal wage growing a cash crop for a wealth land owner? None.
So what about all the poor non-Natives that came to the colonies willingly? Well, under the law of the time most of them became property owners. In fact that is the only reason most of these people were willing to risk a dangerous Atlantic crossing into a much less civilized world than they had known in Europe. Because unlike in Europe where land was heavily concentrated in the hands of the few, land in America was plentiful. The dream was you staked out a claim and worked that land on your own. Some were trade craftsmen or merchants obviously and went other directions, but those people obviously had no interest in working for a menial wage in a balmy Southern climate so someone else could grow a cash crop.
Here in modern America it’s hard to understand, but there were lots of real options in colonial America other than “work for someone else” and “starve.” Most colonists were either property owners, tradesmen, merchants, or were “up and comers” like indentured servants or apprentices working their way to being something better. Now, some of these property owners lived on meager plots in squalor, but they still had their options in life.
When land and individual opportunities are so freely available, people will not go work horrible wages in terrible conditions. Let’s say here in America, you could generate say, $30,000 a year off the land you live on and that most Americans could do that. Not too realistic these days, and some people don’t own land, but in colonial America that was fairly realistic a concept.
If you can do that, would you go work at McDonald’s for $7.25/hr and get cussed at by rude customers and treated like shit by a petty tyrant franchisee? The answer is no, no one would. The only people who’d work at McDonald’s would be teenagers and others with no property (which again, in colonial America most who wanted property and weren’t indebted or indentured in some way could go out and get it.)
If not for slaves tending tobacco, indigo, and other early cash crops the reality is they never would have been grown in large scale. Small holding farmers would have grown what they could, but they’d all be growing it for themselves.
After the Revolution when the primary cash crop became cotton, it was basically the same deal. The cotton boom simply wouldn’t have happened in the 19th century if not for black slaves. Take all of them away ( or free them all) and the labor just isn’t there, period. People could go out and homestead until like 1890, or go up north and work in a textile mill or etc for a certain wage. So any wage that would attract people to the cotton plantations would most likely make them unprofitable.