Slave based economy means that there are enough slaves to be economically relevant. And that was hardly true for any place outside the Americas.
Off the top of my head, Greece, the Roman Empire, the Ottoman Empire, the Mali Empire, Summeria, the Ayubbid Empire, Egypt, Nubia...
Slavery's been part of economies for the last 12,000 years. Anywhere you found agriculture on any continent in the world, you'd find slavery forming a good chunk of the economy. This isn't even getting into the semantics of slavery 'outside' the economy (e.g. Aztecs taking slaves and sacrificing them wouldn't make them materially richer, but it doesn't make the slavery itself less heinous).
When we discuss how our current economic system is "slave based" it is on the basis that workers exist to make the " owners" wealthy, while the workers are never able to move up in position or wealth accumulation. They do all the work, but only the " owner" is the one who increases their actual wealth.
Plantations provided food and shelter for slaves, but the slaves never changed their position to be able to obtain wealth. The same can be said of our current economy, not just in the US, but look at much of the world. If only the owners or executives of said businesses are the ones actually increasing their accumulated wealth due to the work the workers do and the workers are only " just surviving" but not actually increasing their accumulated wealth as well, It is STILL a slave based economy If at the end of a workers life they have not accumulated any wealth, they were financially left off no better than the slaves. OTOH, if the workers accumulate as much wealth as the executives or owners, it is not.
Wealth inequality is a thing, but it's a leap to say it's equivalent to slavery.
Like, slavery's pretty much at rock bottom. Somewhere up above it is stuff like serfdom or indentured labour. Working for a wage might not be glamarous, it might not even allow you to increase your wealth, but it isn't slavery.
One of the first jobs I had was at a car wash. We were literally paid by the minute (which is illegal). Not the best job in the world, but if it was slavery, I wouldn't have been able to say "screw it" and leave the job (which I did). And frankly, if I'm working for an employer, I'm not really concerned if they're making more money than me. They're the one who starts the business, they're the one who makes the downpayments, they're the one who takes the up-front risks.
CEOs being paid 200x than their employees is one form of insanity, but if I go to work for someone, I'm not overly concerned if I'm paid less than someone higher than me. And it isn't any different in local government either.