Everyone is welcome to her or his own opinion. But personally, I'd call this good IT, not bad.
Instead of potentially crashing the site, Disney only allows a certain number of people to access the databases at the same time. And instead of a generic "come back later" message, they seem to be placing people in a queue.
Yes,
scrappinginontario is correct.
Disney+ is completely separate from Disney World's IT folks.
I was on the Training Team for the resort reservations upgrade that happened with the MyMagic+ initiative. Without getting into proprietary information, I can say that Disney was limited as to what they could do to modernize their systems. The reservations system needs to be able to accessible to third-party systems that travel agencies and airlines use. Those systems (GDS = Global Distribution System) have been around for decades. As such, Disney had to design around the requirements of the GDS.
In contrast, streaming video is "new" technology. My current job involves displaying video content on websites. As I understand it, streaming video far less complex than the various components required on for the travel-related systems to run.