Scenes jump from one another with no transition, but there has been time lapses. First instance, Paul has to cross the dessert...so they show him being sent out and Chani watching him. Then it skips and Chani is with him, then skips again and they're back in the community. There's so many examples of that, and a lot of the setups are missing. Now if it's not important to show him learning to survive out there, there was no reason to show it to begin with...what to get a scene with no dialog between he & Chani?
Dune isn't actually that simple, which is why it was always deemed unfilmable or better as a series/mini-series.
To answer your other question about the book, the basis for it is entirely political. Overall, EVERYONE has an agenda. So, everyone is using their resources and alliances to gain positioning over the others. It's also favors intelligence over brute strength. "It is by will alone I set my mind in motion." The world itself values intelligence, status and manipulation. Even in the fights and wars, there are reasons why certain weapons are never used. Everyone is playing chess, but everyone is on the board, so your pawn is a rook/king/knight in another's game, and a King/Queen in theirs. It is dense though, and wordy. To put in a modern comparison, it's Game of Thrones but if everyone was on the Limitless pill. The overall theme is pretty much to never trust the charismatic "leader" for they all serve themselves. There's also heavy criticism against putting everything into religion. While it does serve as a place of comfort and power, it's easily exploited. The Fremen are pretty much irrelevant to the story. If Leto hadn't died, they would still be used for the same purpose - an alliance to fortify Arrakis and control the most valued resource in the galaxy, and Leto was never on the board as "the chosen one." They're so irrelevant that no one cares about the rest of the planet.
Even with House Atreides, Leto was not married to Lady Jessica. She was his concubine, and he was not married for the sole reason to keep his options open to form alliances with other houses via marriage. In reality, you can figure he was never going to do so, but that was also an option. There are also instances of Lady Jessica having her own plans, using Leto and Paul, but going against the plans of the Bene Gesserit who gave her part of the plan in the first place. And take the "prophecy"; the Bene Gesserit started the prophecy and planted the seeds over generations/centuries until they could create their "Chosen One" with all of the traits they said in the prophecy, just so they had control over everything.
