In response to the above:

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Maybe? We're not shown much of Fremen industry to inform us either way, and the plot point from the books about the Fremen bribing the Guild with spice to keep satellites off Arrakis isn't really brought up here. What is explicitly said in the film is that the South is a much, much harsher climate than the North ("no-one can survive there without faith"), hence my assumption that it's more resource-poor. Certainly it's poorer and less important from the perspective of the Imperium, since the North is apparently where all the spice harvesting happens.

Regarding the idea that Northern Fremen developed their cynical attitude from contact with offworlders, or from interaction with Jessica and Paul, that's possible, but is it ever really stated in the film?

I actually wonder if, in an earlier version of the script, Chani was Kynes' daughter like she is in the books. It would go quite a long way towards explaining why she is so averse to the idea of the Fremen being "afflicted with a Hero."