Dune

How did he go from wanting simple revenge, to embracing his role has Jihadist entirely in what felt like a scene or two?

Being madly in love to marrying the emperors daughter? why? Also more annoyingly after telling his followers he'd lead them to Peace and foreshadowing being stood on the shores of an ocean, I'd assuming the final scene was Paul leading them back to his own home planet. But a casual google to understand some other vague plot points told me they were actually off to start an intergalactic Jihadist war? I didn't take that from any of the scenes prior at all

it’s a combination of a flaw of thinking prescience is a perfect vision (literally nullified later by no-ships) and also the large assumption that the jihad was inevitable due to the seeds of the prophecy of Lisan al-Gaib being seeded by the Bene Gesserit. Combined that with the whole kanly thing against the Harkonnens and it became a damned if you do damned if you don’t situation.

Also, Paul is distinctly not a hero and one of the major driving points, especially in the sequel books, is that he’s actually the antagonist.

Paul has enough prescience to know that there is a potential future where he causes an intergalactic war. At the end of the first film he rejects this path - hence he kills Jamis in the duel, rather than learning from him as the visions guide him to do.

In the second film, he finds his place with the Fremen, and even finds love. This is enough for him - be a freedom fighter, work with his friends against the Harkonnen through guerilla warfare. He continues to have visions of what will happen if he “goes South” and follows his mother, that being once again that billions will die. As before he rejects this future and tries to stay north - but after the attack on the seitch he realises he must depart.

He ingests the water of life, likely believing it will either kill him (as everyone says it does) or “unlock his vision” and allow him to see a solution. And of course it does the second thing, partly thanks to Jessica grotesquely forcing Chani to intervene against her will.

Ingesting the blood works. However the consequence of this new ability is that it fundamentally changes Paul. He knows the futures available and his only option for survival is to become the Fremen hero and instigate the war. So that’s what he does. He takes advantage of the Bene Gesserit legends and manipulates the Fremen into doing what he wants, knowing it will lead to a huge number of deaths. He is now utterly ruthless, transfixed on the path to the future he sees.

I think it’s sad. In fact it’s almost a tragedy, which is why after the second film I left the cinema feeling profound melancholy. I love it!

Reluctant but then is forced into extremism through external factors.

Those external factors being; become the reverend mother or die, and then her path to survival is opened via worm blood plus the talking fetus