This is an interesting conversation. It reminds me of an astute commentary I read from Joe Rohde on Las Vegas. He pointed out that Las Vegas and theme parks have important similarities, but also striking differences.
In Las Vegas the elements of the city are in competition with each other. Each part of Las Vegas is trying to catch your attention so you spend money and time at their venue. It's a clash of corporate titans trying to appeal to your attention. By contrast, well designed theme parks are designed to reinforce other parts of the experience. For example, Cinderella Castle is not in competition with Main Street USA. The two are designed to harmonize. Cinderella Castle would be a worse experience without Main Street USA and Main Street USA would be a worse experience without Cinderella Castle. A personal favorite example of this concept is the Matterhorn and Sleeping Beauty Castle. The two look like they're made to be together. Because they were! (Well, Matterhorn came later but still
).
At the same time it would be foolhardy to dismiss the artistry and sophistication of casinos and other Vegas venues. Rohde himself expressed his admiration for Vegas. The art of grabbing attention and appealing to the senses is no trivial thing. It's easy to scoff at the casino, but it would be doing a disservice to the craft. They know exactly what they're doing and have mastered their vocation. And as the OP has noted, Vegas has remarkable and awe-inspiring sites, sounds, and tastes. It really is extraordinary!
It's not my cup of tea. I much prefer the curated theme park experience. However, I am not about to mock or belittle another form of spatial entertainment. To each their own!
On Epcot vs. Vegas I would make this observation. As originally developed, Epcot (or should I say EPCOT Center) was designed to blend together. Every pavilion was different, but each was part of a grander whole. Nothing makes this more clear than at night when all the pavilions of the nations light up in one grand vista! World Showcase and all of Epcot were one narrative. They were designed to help make people optimistic about the future and feel engaged in human story. By contrast, Vegas has no narrative or purpose. The parts of the whole are disjointed and completely unrelated.
In recent times, both Imagineering and management have lost the discipline and competence to maintain a story across the park. What connects Guardians of the Galaxy, the Moana fountain thing, and the rat ride? Epcot is becoming less and less coherent. So in a way Epcot is becoming more like Vegas. Not optimal. Not because Vegas is bad, but because Epcot was distinct and special.
Anyway, I'd like to thank the OP for the interesting prompt. Cheers!