"Movie too quick movie too slow" these diametrically opposing views are killing me.
Liet Kynes, Dr. Yueh, and Gurney Hallack all could have been built out a lot more, their characters were deeper in the book. With Kynes especially, by the time she dies (he in the book), you really fukking feel it because she/he was probably the most noble person on the entire planet.
The problem is that that IS Paul. He's a super over-trained, sheltered kid who has hardly even left the palace. At this point in the book he has exactly zero charisma. He has no legitimate reason to have developed charisma, he's never been a leader of men or even had any normal social interactions his entire life, it's just been constant training and royal family functions.
The film absolutely had to end there, if you know the book it's impossible to end it any other place. I think they could have done two things better to have made the first film feel a bit more complete.
#1: They should have shown more training. The way Paul has "earned" it is that he's a specially bred genetic unicorn who has been trained as a fighter by the greatest fighters in the empire, trained as a human computer by the most renowned mentat/assassin in the empire, and the only male ever trained as a bene gesserit. They barely showed a touch of his bene gesserit training and a touch of the fighting training. I really think they should have shown more of that to develop exactly how well-trained he is (apparently they cut a clip of him training with Jessica). That the reason he beat Janis - Janis is a true fukking KILLER in the book, and the only reason Paul defeats him is because Paul has been drilled better than any human ever had been. If they had done more training and played it up a bit more, they could have shown how special he was better than just telling you he was special.
#2: I think the ending would have worked better if the Janis fight felt more high-stakes. They should have spent a little more time building up Janis's character, and made the first part of the fight more dramatic so you got more worried that Paul might actually die. Once Paul gets comfortable in the fight it's true that it was easy for him, but it was his first true fight with life on the line and they could have made more difficult for him at the start. Then I think it could have been a more satisfactory end point.