Dune (book and movie) is open to interpretations.
I see the Houses of Dune as intergalactic corporations. They are more about business than family and power, which is the exact opposite of the Houses of Game of Thrones. Do you disagree? OK. I can live with that, but stay with me and hear me out.
Money makes our world go round. Spice makes the Dune universe function in almost every aspect. If you want to travel through space, you need - Spice. If you want to live longer, you need - Spice. If you want to have "useful visions," you need - Spice. Have I left something out?
Now, you may say that I'm exaggerating when comparing the Dune Houses with the space corporations. Are you sure? What are our "space billionaires" doing right now? How do you feel about the House of Musk, or House of Bezos, or House of Branson? What if we're witnessing the birth of galactical business empires?
He's carrying all the weight of the unimaginable responsibility on his shoulders. Could he avoid the "gift" of being the new "manager" of Dune? Could he say thank you, but no thank you to the Emperor? Are the wars between the Houses over Dune avoidable?
Well, here's a nice comparison on a smaller and bloodless scale between Elon Musk and Jeff Bezos. Currently, the lawsuits and tweets are the most dangerous and powerful weapons they're using against each other.
Duke Leto should've known better. How many examples of business rivalry gone too far do you know about? Does any of these sound familiar to you: "winning is everything," "whatever it takes," "everything is allowed in business wars," etc.? The modern business rivals would make Machiavelli blush.
Time to sum up the terrible business leadership mistakes made by Duke Leto:
1) Ensuring absolute loyalty should've been his top priority. He had every right to be paranoid. He wanted to be loved more than feared, and look where this attitude got him and his House.
2) Oscar Isaac was the perfect choice for Duke Leto, no question about it. But, the real question is, was Leto Atreides the right choice to be a Duke? While having the most important conversation about the future of their family and duties with his son Paul, he hesitates to put it mildly. He says: "A great man doesn't seek to lead, he is called to it." That's a nice quote, but nothing more than that.
3) He was already late with his prep homework. Aquaman as a scout in the desert. Yup, the results were exactly as you might have expected. The intelligence pieces of information he got were simply too optimistic and incomplete.
4) The legendary Spice harvesting scene that went wrong speaks volumes about Duke Leto. It's heartwarming to see him as a hero who saves the day, and puts the lives of his staff above profit. Unfortunately, this scene also illustrates his lack of strength to make tough choices and necessary sacrifices for the greater good. OK, it was "just" one harvester we're talking about, but there's more to this rescue story. These things don't happen in the heat of the battle. You have seen other movies. How many soldiers had to be sacrificed to win a strategic point or the war itself?
5) Duke Leto looks for allies in the wrong places. If memory serves me right, there were 31 Houses of Dune. Of course, not all of them were as noble and powerful as Atreides, Harkonnen, or Ordos. Fremen are the cool guys, but every new "governor" is nothing more than a "colonialist" interested only in exploiting Spice in their eyes for the right reasons. Leto was wasting time with Fremen, plain and simple. He should've looked for allies elsewhere. He should've stretched his diplomatic muscles with the third noble House in Dune universe against the House of Harkonnen that played all the right moves against him.
Even if Harkonnen had somehow accepted to deal with the "transition" in a civilized and peaceful way, and the Emperor had nothing more than pure business motivations, rest assured that Dune under Duke Leto would struggle and eventually be forced to declare "bankruptcy." In a hypothetical scenario, the Emperor would have said something like, sorry Duke Leto; you had your chance, Dune goes back to Harkonnen or some other House.
When the fate of the entire Empire depends on the regular and adequate deliveries of the essential "product" or call it what you want, you have to be a practical and ruthless leader in a business sense for the complex and fragile system to work as expected. My personal impression was that Duke Leto was more of a dreamer than a doer.
Duke Leto might have been your favorite fictional character, but I'm not sure that you would like and support him as your business leader.