I don’t think you found capacity but more that you found Universals expectations for busy day guest count at the new park.
For reference Universal Studios Hollywood can hold more than 40,000+ guests at max before lockdown, and done so several times over the last year.
Magic Kingdom can do 65,000 before phase 1 capacity is reached and they have criteria for entry. Max capacity before lockdown is presumed close to 100,000. Averages almost 57,000 guests a day from attendance figures.
Epcot max presumed 95,000.
Animal Kingdom max presumed 65,000.
Hollywood Studios 75,000(I believe when park is fully opened though)
Universal Studios Florida and Islands of Adventure are hard to find but average daily visitors by attendance look to be close to 30,000.
Enjoy