The mode of production is never human nature. Human nature is a factor, but the mode of production is something that is socially constructed and subject to material constraints, like tools and the environment in which people live.
But socializing and sharing empathy is virtually universal, and the impetus to share food or shelter or community is something that capitalist society teaches us to avoid. So one of the things we strive for through the abolition of capitalism is the restoration of human connections and care that are currently robbed from us. So I can totally see where you are coming from re: the extent to which the communism we want to build constitutes a return. But it is even more a step forward, a transformation into the future constructed from the bones of the present.
Re: what Marx called "primitive communism", which we might better call egalitarian societies based on hunting and gathering and sometimes agriculture, such societies have actually existed everywhere people have lived. You can find clear historical examples of such societies in the Americas and Australia, yes, but also in the Middle East, Ukraine, Great Britain, Ethiopia, Pakistan/India, China, etc. As you mention, any of these societies did not have written records or they were lost, but we can understand how they lived based on their homes, food, tools, dress, cohabitation, and spatial distribution of all these things.
Capitalism is not about individuals being greedy. Calling capitalists greedy is like calling fish greedy for needing water. The capitalist system requires constant profit maximization to prevent firms from crumbling, the capitalists are tasked with ensuring this, generally by (at first) maximizing exchange value of their product and minimizing costs (usually labor), then later using monopoly position to charge economic rent. In the heart of empire, financialization has meant trying to skip the first step via large financial investment up front, like with tech monopolies. The system itself forces exploitation, dispossession, colonialism, and ultimately crisis and war.
Historical empires conquered for reasons we often don't really know specifically, as the accounts we have are written by victors with limited access and understanding. But ancient peoples were just as sophisticated as us and subject to material forces as us, so it was certainly not just being greedy. The economic base can force hands, for example. The Roman slave and debt system was unsustainable and required debt jubilees and war and invasions to be maintained, for example. For the ruling class of Rome, was maintaining the empire only greed or was it what they were taught to do as the moral and right thing?