Animal Kingdom is severely underbuilt. 4 E-Tickets only. The most popular one has atrocious capacity.
Hollywood Studios is severely underbuilt. It's most popular E-Ticket is an operational nightmare.
Epcot isn't underbuilt but rather an issue of no significant updates. Living with the Land has great capacity, but it's not popular. Same with Nemo, Mission Space, etc. Everyone wants to ride the same 4 (SSE,Test,Soarin,Frozen) rides.
Magic Kingdom is underbuilt for the attendance it receives. There's no reason why that park should have less attractions than Disneyland. (Don't kid yourself, most guests can care less for Country Bear, Tiki, CoP, PeopleMover, Presidents)
Also, Tron is going to have atrocious capacity. Seating 14 guests, and dispatching at a rate of approximately 45-50 seconds it'll have an hourly capacity of 1,008 to 1,120 an hour. (Hopefully they can get those dispatches faster)