There is no difference in the outcomes between the slave revolts you described and communism. Communism has been what you have described - a group of people becoming new slave masters. The Communist rulers living lives of extreme luxury and opulence at the expense of the common people. Yet still, the sentiment among the people that drove those communist revolutions was the desire for a more just and equitable society. While we can't read peoples minds from thousands of years ago, I do not doubt that the common slaves held that exact same sentiment.
You're conflating the results with the ideology.
Communism is an ideological goal of an egalitarian classless society where each is given according to his need and from each according to his ability. That communism in practice has always resulted in autocratic states or just total implosion or evolving into capitalist societies- is just a product of the inherent instability of communism. Because capitalism is a self-reinforcing stable system and communism is self-destabilizing.
All the historical slave revolts, popular revolutions, regime changes, etc from thousands of years of history prior to Karl Marx were not driven by any ideology remotely similar to communism. They can result in the same outcomes, but that's because those are the same outcomes
every power vacuum develops. When enslaved people revolt just they hate being enslaved and want to be the new masters, it isn't the same as a radical philosophy saying we should have nationalized joint ownership of production and distribution so everyone is given equal shares.
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In the present day, the belief that humans are either the male or female sex has been described as Fascism by the ruling class, so I'd say it being resilient to definition is an understatement. Simply it is of course the principle that there is strength in unity and weakness in division - a principle that is self evidently true. The Roman Republic was significantly more "fascist" than its rival at the time, Carthage, but it was very far from a democracy. The Roman Republic was a hereditary aristocracy - only Patricians could be senators, and senators were appointed by Censors, not elected. It was however significantly more democratic than rival states at the time, with plebs having some enfranchisement in local affairs. The ascendance of Caesar and his democratic ideology made the Roman Empire significantly more democratic than the Republic, and saw the abolishment of heritidary castes among our civilization. Carthage was however nearly a pure oligarchy - the rulers were merchant lords, and the bulk of their armed forces were mercenaries, contrasting the Roman Republic which raised armies from the free citizenry and trained them through institutions. The oligarchic system was nearly wiped off the planet with the doom of Carthage, and then the doom of the anti-democratic Brutus and friends, but has seen a resurgence in the past century+ with the present hegemony of an ever-progressing Jewish oligarchy - a system that unfortunately persisted after its just destruction following the revelation of Christ.
All in all a great description, no society ever cleanly fits a label in the present era. Ideas persist through centuries, nearly all of our (Western) institutions are still Roman.
I don't think all the exaggerations and conflations and misuse of fascism as a term actually change the underlying concept, which stays the same it ever was. After all, language is just a tool to express concepts and serves only when it is mutually intelligible. People babbling about anyone not agreeing with their gender ideology dogma being fascists, well that just makes them idiots, it doesn't change the philosophy of fascism.
Even if Rome wasn't a pure fascism, the elements were right there. The bureaucracy of government was absolutely set up for the popular benefit of the citizenry. Laws were passed and public works commissioned not for the benefit of the aristocracy or to subjugate the masses, they were for
the citizens. That identity remained intact for nearly a thousand years. The citizens of rome worked together for the common good of rome, creating infrastructure and armies and technology that surpassed every contemporary and remained a zenith for centuries. The aqueducts weren't designed to bring water to the senators, the colosseum wasn't built for the amusement of the equestrians. The soldiers could kill emperors and rise new ones from their ranks. Every man who could say he was a roman citizen benefited from roman achievements and could enter a bathhouse or import wine from overseas.
The biggest mark against Rome being fascist is the lack of single party totalitarianism, which throughout Roman history was only sometimes the case. Rome was notable for many periods of coexisting dueling ideological groups with opposing political factions. And it had a few flareups like the catalinian conspiracy or triumvirate's proscriptions when the opposition was crushed but even then there was no national identity along a single ethos. Instead roman identity was more centered on the claim of shared civic privilege rather than shared civic virtues, identity or ideology.
Still the root has to be, fascism is about the strength of a united society that works towards a common good for the people, intolerant of dissent and opposition. That can exist in societies with or without class distinctions, autocratic or democratic, but it does require a coherent national identity like citizenship and it does require the exercise of power to be rooted exclusively in an ideologically homogenous body.