100% True.
But this was also one of the problems with Kirby's origin for the Eternals, because there were civilizations that pre-date the Greeks and Romans. Indeed, some of the Greco-Roman gods are derivative of other gods worshipped in other regions. In order for the Celestials to have experimented at the "dawn of humanity", the timeline simply doesn't work. The Eternals that we know today would have needed to be the distant ancestors of the proto-humans that the Celestials experimented on AND there's no way that the vast majority of the Eternals would look like Greeks or Romans. The only way that Kirby's origin works is if there are hidden tribes of Eternals hailing from other continents, perhaps existing like the gods themselves in dimensions adjacent to Earth's. As depicted, the Eternals population demographics doesn't seem to speak to that at all, unfortunately.