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> Thus it seems incorrect to talk about a “universal speed limit of causality”. Am I missing an essential concept?

Probably. Why would points becoming more distant due to expansion of space be a counterexample to the speed of light being a limit on the speed of causal propagation? Spatial expansion doesn't move anything, so it can't propagate information.

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It doesn't move anything, but it does mean that things that are now far away used to be closer, and therefore had the ability to affect us, but now don't.

Not that it matters, because the speed of light is still the limit: if they could influence us when they were closer, that would have happened by now.

> Spatial expansion doesn't move anything, so it can't propagate information.

It certainly moves matter-energy in different regions of space with respect to one another.

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