How was the Earth created? Bits of stardust and rock fragments don't arrange in a nice, neat disc-shaped formation,
Turns out that scientists are not 100% sure about the nature of the round Earth's creation either, but it involves a spinning disc of gas and dust condensing into several smaller spinning blobs of gas and dust that eventually collapse under their own gravity. There's a theory as to what sort of planets can form at different distances from the central star, but several of the recently-discovered extrasolar planets break the rules, so it's likely that some refinement of the theory is needed.
Anyway, I don't know why you think you get to say, "Bits of stardust and rock fragments don't do such-and-such." Turns out we aren't entirely sure what they do. But it's not any less plausible to me that disc-shaped clouds of dust might condense into disc-shaped planets... not to point out the obvious, but initially it feels like it's
more plausible.
... suddenly get an atmosphere by unknown means,
Unknown? There seems to be this assumption amongst REers that nothing on the FE can be at all like anything on the RE. You end up getting misguided questions like, "How can there be plate tectonics?" Duh, maybe there's still a molten core, maybe there's still plates, maybe they still move around. Why wouldn't there be such things on the FE? Is it part of FE canon that the Earth doesn't have these things?
RE theory stipulates that the original atmosphere was leftover gas from the original cloud from which the solar system formed, and chemical and eventually biological processes on the Earth reshaped the atmosphere's composition to be what it is today. Why can't a flat disc have an atmosphere for exactly the same reasons?
I suggest that REers who want to ask FEers to explain certain phenomena are obligated to:
1) Explain the same phenomena using the RE model, and
2) Demonstrate that the very same explanation doesn't hold in the FE model.
-Erasmus