1. Spice on Arrakis is a parallel to oil in the middle east. Another point to this is that the technology is not really important to what Dune is about. The other thing is there are no computers/AI/thinking machines.
2. The Emperor is threatened by the Atreides for two reasons I think are mentioned in the movies. He is supposed to be jealous of Duke Leto, because he is a popular voice among the Houses and people admire him. The Atreides are also supposed to be great and loyal fighters and the book I believe describes Gurney Halleck and Duncan Idaho as some of the best fighters.
3. As far as everyone being miserable I don't really know how to respond. I think Frank Herbert was a cynical kind of person and I think that is reflective in the fact that everyone is vying for political power. Some just do it in different ways, Harkonnens are just violent, Bene Gesserit do their bloodline and body control training, etc.
4. As far as Paul beating Janis I think this is something in the book that was left out in the movie is that the Fremen are excellent at surviving the desert and knowing the desert better than the current occupants of Arrakis. They are not necessarily warriors at the beginning because if they were they would have already gained control of Arrakis. Meanwhile Paul has been highly trained by some of the best fighters in the universe.
5. As far as "angsty teenage edgelord boy" I just can't agree with that given he is having vivid visions of billions of people dying across the universe because he gains power. These visions are fueled by spice which is psychoactive and everywhere on Arrakis including in the food. As well as the worm poison which is highly concentrated spice so even more psychoactive.
6. When the Atreides left Arrakis they took everything including the atomics which all the houses have.
7. The Emperor comes easily because everyone has underestimated the Fremen and they are not aware that Paul is Muad'dib.
8. The ease with which the Emperor is defeated is two things I think. Frank Herbert does not do action very much in the books so it was up to Denis Villenueve to add in the action scenes. The other is that the Fremen in the book are trained by Paul and Jessica to become fighters. This is left out in the movies. Between that training and the hardened nature of their people having spent centuries on Arrakis, they are now the best fighters in the Imperium.
Final note: I don't think we have to compare anything to LOTR. Some people like magic fantasy land and some people like a cautionary tale about messianic figures and a cynical view of humanity in the future. Some people like both. Idk.
Also, want to add that the Tleilaxu do try and grow sand trout in other deserts in other planets to replicate the spice growth outside of Arrakis. We as Bitcoiners should appreciate that absolute scarcity is not only relegated to digital domains. And it’s science fiction, makes for more thrilling scenarios. In this one scarcity is that sandworms seems to grow in Arrakis and due to that spice happens to be there.
Also I want to say that sand worms are not native to Arrakis but I could be wrong