With 24 hour event it sounds like you were not there, unlike myself who was there for almost the entire 24 hours. Attractions during the day were not manageable. It was a mad house by 9-10am. The only time it became manageable was after all the nighttime entertainment was over and people left around 11pm. And even then new people were not let in until after 3am. So those manageable times you spoke of was when the park was empty from 11pm to 3am before they let new guests in from 3am-6am.
Also where are these large scale waiting areas you speak of in Disneyland? There is only a finite amount of space at Disneyland on Main St, Hub, and NOS for people to stand. This is not extra capacity. This entire space is counted toward max park capacity.
From what I can tell you seem more experienced with WDW and how Magic Kingdom is setup, its not the same at Disneyland. There is not some large scale waiting area to throw extra bodies. In fact they had to build overflow paths behind the Main St shops just so people could get in and out when Main St is blocked during nighttime entertainment. And if you've ever been during nighttime entertainment you'd know you can't get to certain areas of the park because they direct you away.
I'm a former DL Passhole who visited the parks more-or-less weekly for several years, far exceeding the dozen-or-so times I've been to WDW. I know people who have worked in operations, both on the ground and at the planning level in TDA. I'm plenty familiar with how DLR operates, handles crowds, and the specific peculiarities it has to deal with.
Those large scale waiting areas include the ROA riverbanks (holding around 9,500 guests), the hub (roughly 12,000), Main Street and the parade route (which vary, depending on the setup). Yes, using those areas bottlenecks the walkways for people passing through and create unique traffic patterns. Yes, there are other complications. But that's not the point.
The point is that they take the otherwise-uneventful walkways and turn them into places that people want to spend a large amount of time. When you have 20,000 people waiting for shows, they free up space for additional people in the rides, queues, restaurants, and shops, to get their 7.2-ish "things" accomplished in order for them to enjoy their day. Yes, it may take slightly longer for people to reach their ultimate destination through the crowds (I've often gotten routed in odd ways, but never been unable to reach any location in the park), but ultimately it's a wash (or even advantage) because the queues are so much shorting during those times, even though more people are in the park than earlier in the day
Disney knows that they technically can fit more people in the park, but they also know that once they drop below that certain number, satisfaction and per-guest-spending drop dramatically. Happy guests spend money and tell their friends to visit the parks; angry guests don't spend money and tell people to stay away. Disney knows that they can get more out of the park by keeping guests happy, which means artificially limiting the capacity and adjusting it throughout the day to reflect the number of things-to-do at any given point (whether that means planned refurbishments, additional entertainment, or unplanned downtime)
Anyway, my original point still stands: the 24 hour event did *not* use the "normal" park capacity that they would use on a typical peak day, because they knew that people weren't there for a normal experience. Disney can and often does limit entries far below what the Fire Marshal permits. I don't doubt that the Fire Marshal was involved during that event, but I also know that they don't allow nearly that many people into the park on a normal day, because on a normal day they care more about guest satisfaction metrics than they care about letting as many people as possible see the premiere of new entertainment
