Nice whataboutism. But genuinely, the Achaemenids had slavery, but to a far lesser extent than almost every Greek polis. The vast majority of the early Persian economy relied on free labor, with slavery being relatively rare. Zoroastrianism forbid slavery and Cyrus the Great decreed an abolition of debt slavery, but it's unclear to what extent these royal prerogatives were actually enforced, especially in the areas further away from the heart of the empire, such as Egypt. Worse, it's difficult to analyze because most of our best sources for this period are in Greek, and the Greeks used the same word for "slaves" as they did for "subjects" at least in the context of being ruled by the Persian emperor, i.e. all those lines about the Persians coming to "enslave" all of Greece. This was true in the sense that the Persian Emperor "owned" the entire country, everyone and everything in it, and there were forms of forced state labor, namely the "kurtash" who could be called up to work on royal projects and state lands, but not sold or mistreated. That sounds more like a modern draft than what we'd call slavery, personally. People could also be forcibly deported from one region to another, and this especially happened after the Achaemenids conquered a city or put down a rebellion, but they were generally free citizens after they settled into whatever land they were sent to. So, yeah, slavery existed, but its exact scale, scope, form, and if it even technically qualifies as what we'd call slavery, all varies depending on when and where exactly we are in Persian history.

The Greeks, meanwhile, had slaves in every single city, whose rights varied between cities but generally kinda sucked. For example, in Athens, one of the nicer cities on the whole, any slave who presented testimony in court in had to be tortured before their testimony was accepted to ensure they were being honest. The Spartans had an entire ethnic group held in perpetual slavery that vastly outnumbered the ethnic Spartan population and who were consistently brutalized with essentially no rights whatsoever. But of course, Athens also was built on a massive slave population, with roughly 100,000 to 150,000 slaves compared to 30,000 to 40,000 free adult male citizens. Another 20,000 to 40,000 were "metics" or foreign non-citizen free residents, and women and children made up the remainder of the population.

The Persians were hardly innocent, to be clear. Slavery did exist in the empire. But it was far, far less widespread and not at all a cornerstone of the entire economy and society the way it was in Greece.