The funny thing, that at least at
Disneyland but I think it might be the case in WDW too, is that "in park capacity" has dropped in the last decade. DL used to be around 80,000 but has dropped to around 60,000.
The main factors that determine park capacity are
A. attraction capacities
B. queue lines
C. shops, restaurants
D. corridors, walkways
Now take a look at a park like Epcot. World of Motion was replaced with Test Track. WoM had a ride capacity of 3,240 people per hour. Test Track's is 1200 people per hour. Horizons has a capacity of 2,784 people per hour, Mission Space most likely will be less than that.
Or take the Magic Kingdom where over the last decade 20K, Carousel of Progress, Skyway, Timekeeper have all been removed without a replacement attraction. That's a lot of lost capacity. If Park Capacity = A+B+C+D, and C,D remain constant, and (A + B) decreases [closure of an attraction] then PC decreases.
And then, Disney introduced FASTPASS. On one hand great benefits for guests, but look what it did for the capacity of the park. It dumped thousands of people out of queue lines and into the walkways. If the lenght of a Splash Mtn queue line for an hour wait previously would have been 1000 people, post-FASTPASS that same hour wait means only 300 people are in the queue line. B decreases. And since A, C, D all remained constant... PC decreases too.