While I no doubt that Disney has slowed construction to spread costs in the past, I also think it reasonable that there are other factors. The first being Disney's propensity to spend the big bucks because they can which makes them a bit bloated.
Several insiders have mentioned Disney changing specs on the fly as something is being built, which costs money and time... but Disney does it anyway.
Another factor is spreading out openings. That wasn't much of a concern in the past decade when hardly anything was being built, but now that there are a lot of projects at all four parks (and DS, and waterparks, and resorts), WDW would want to make sure something new and big is opening each year. That's why I think TRON and GotG Coaster are taking so long. TRON to time it with MK's 50th, and GotG to provide a counterbalance draw from MK. We've been told by our insiders that WDW sped up Rat's opening so that there's something in 2020 that will open -- imagine that, a project going faster, not slower.
Also, one needs to be careful of bias in quoting construction timelines. I've often heard that the Potter Lands were built in 2 years while Pandora in 4 years. But that two year difference is a big ol' huge lie. The Potter Lands took two and a half years and Pandora three and a half years -- that's just a one year difference, not two. But, for some unknown reason, certain people will round down for Universal and round up for Disney.
Here are some stats:
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