That's pretty surprising and breaks my mental model of how these chips perform. Do you think that's because they don't have the raw FLOPs, something inefficient in the Apple/Metal rendering pipeline, something about Civ VI and how it was converted (i.e. x86 or DirectX emulation), or something else entirely?

I've had no trouble with a (base) M4 mini for regular dev work, though I compile remotely and haven't played any games on it.