Hold on a second here:
In the Dune Empire, all of the Houses are violent and self interested - Atreides included. They are not above Chalmurky, and the fact that Leto's father died bullfighting should tell you a little bit about violent mindset of the people of Caladan.
There is two primary contrasts made - ethics and cruelty. The Harkonnens are unethical and cruel. They are breaking the rules, but are also terrible rulers and human rights abusers. Unlike the Atreides, they have slaves, and will kill just about anyone for pleasure.
Shaddam is not particularly cruel, though entirely ruthless. But he is not depicted as someone that enjoys torture or death.
The fulcrum of Dune is that the Atreides have become two things - immensely popular in the Landsraad. And enormously proficient in combat - due to Halleck and Idaho. The Emperor, who has no male heir, is not necessarily popular and maintains power in large part through the threat of his Sardukar. If it became generally known that Atreides fighters could beat Sardukar in a fair fight, the Landsraad may turn on Shaddam by combining their military and economic forces to oust his house as imperial seat. Which is pretty much how the Shaddam's ancestor became emperor in the first place.
So, though he likes and admires Leto, Shaddam makes a decision to destroy the Atreides to maintain his power and send a general warning to all Houses about rocking the boat. The problem is that his fear of the Atreides army doing favorably against Sardukar leads him to make the unethical decision to secretly and illegally back the otherwise legal attack of the Atreides by the Harkonnens.
This is an interesting moment, because Shaddam's close council is a high level Bene Gesserit, who has a vested interest in the Atreides. However, Jessica screwed things up by having a boy, so the Bene Gesserit may have felt that trying to influence the Emperor was not possible or not worth it considering other available gene lines. So they did their best to warn the Atreides of the peril, and stepped back. What happened after that was largely affected by three things - Paul surviving, and being the KH; Atreides policies attracting the interest and respect of the Fremen; and the Fremen being potentially much more dangerous than the Sardukar (Atreides/BG training and command being the missing piece).
The BG has used the noble families as breeding lines, largely because the politics of noble house marriage are much more easily manipulated and tracked than regular people, but at no point does any commentary suggest that Shaddam, Irulan or even Ghanima's husband have any of the strongest KW genes. So I would disagree that Shaddam is anything more than very smart, ruthless and unsentimental in his quest to maintain status quo.
I haven't seen anything in the upcoming film trailer to suggest that this Shaddam is any different from the book's - except that he looks older than described (spice works wonders).
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