the ancient Egyptians, who thought the sun goes round the earth, could also predict eclipses
That the sun goes round the earth is not more or less right than the converse. It’s a construction of the same system in different coordinates and quite valid.
However, the Oval Earth theory is wrong, and you can’t predict eclipses from it correctly.
More to the point, arguments like this against knowledge from authority rely on implicitly accepting most such knowledge, and only disputing a few choice examples. In Orwell’s story, how do you know about the ancient Egyptians, or what theories the Lord Astronomer espouses, if not from “newspapers and science booklets”? How do you know what astronomical knowledge exists regarding navigation or eclipses? How can you know when eclipses occurred before your birth (to work out cycles)?
If you don’t accept the commonly held theories (because you haven’t verified them yourself), why should you accept the commonly known facts (without having observed all of them yourself)?
I also don’t agree with Orwell that Round Earth theory is “exceptionally elementary information”. It really doesn’t directly influence the life of the average person in any way; we don’t normally make decisions predicated on the truth of that theory outside of a few professions. It’s just a very well-known piece of common knowledge, in part because some Flat Earthers still exist who deny it, and due to the related Flat Earth Myth about the Dark Ages.
Relying on expert knowledge is a good way to evaluate claims only the first few times we encounter them. If we act on a piece of knowledge repeatedly, this should allow us to directly confirm or disconfirm it. If this doesn’t happen, it’s probably a sign that the purported knowledge or theory is just a marker in a political/social/religious game. We know Oval Worlders are the enemy and so our authority figures always affirm the Round World theory, but this doesn’t have anything to do with the actual shape of the earth.
The world was simple then because we hadn’t evolved greater predictive ability, not the other way around. It’s more complex today because humans have used their predictive abilities to build complex tools and social structures. So our extrapolating hardware is correlated with the modern world in two senses: it was enough to build it, and it is enough to presently survive in it.
True, we would profit greatly from better extrapolating hardware. But this was just as true in the ancestral environment! Extrapolation ~~ Intelligence ~~ Power to achieve goals. Also, better hardware gives a particular advantage in intraspecific competition, so once genes (or other replicators) for it appear, they spread rapidly.
Ours is not the narrative of “how humankind barely had enough brains to cope with the modern world”. It’s the narrative of “how humankind had just a tiny amount of brains more than he needed to cope with his ancestral environment, and used them to build a world so complex that only he could survive in it, to the exclusion of cousin species and of older human genotypes”.