It's the slop-tunnel for all communications. The added bonus of high odds of it completely changing the meaning makes everything worthwhile.

Nah, it's just some harmless sculpture for him to place in his office!

If you want a spoiler:

So... He noticed Netanyahu saying that after Lebanon it's Turkey?

Have you seen the Lower Decks episode? That's what happens.

They have several opportunities to see the Fremen riding the worms already in the book. As you said Leto discovered they were much more numerous than it was widely believed. And that is with just a short occupation before everything happens.

Harkonnem certainly had plenty of opportunities to discover he was underestimating them.

Have you tried books?

Cuba is different from Iran in a very important way: it's within drone-range from the US.

Everybody: "The US is in decadence, it won't be a superpower by the next century"

The Donald: "'By next century!?' Amateurs!"

Genocide is maybe war crime, news at 11!

You can call it a mistake, but how exactly were the Harkonnen’s supposed to accurately gauge Fremen manpower?

Hum... By having any bit of humility and looking.

But that's one point where the book is completely realistic.

Mass transportation should drop the pretenses of being a business and stop demanding a fare from people riding it.

That would solve a lot of problems, and make the system way cheaper.