You're also looking at just construction when you talk about DL being built in a year. It's not like Walt had the idea in 1954, and it was built in 1955. It took a few years of planning back then too. He also had to finish by then, or he would have ran out of money, no bigger motivator than that. Another thing to remember, DL was pretty simple back then. All the technology we use in modern buildings and attractions takes time to coordinate between the architects, engineers and all other involved parties. Not only are the codes more stringent, but the actual things being designed are vastly more complex.
The last thing, the Anaheim Building and Safety Division is not the fastest building department to work with. I've seen plan reviews for tiny projects take many weeks to review, which is significantly longer than other cities would take. Even the giant mess that is LA is faster then Anaheim in my experience. I would imagine it could easily take a year to just get through the building dept on a big project, and that's only one of many approvals they would need to start construction.