Wow, I can't imagine what would happen if there were only 20 good seats for a show at Disneyland. People lined up for hours to get a good seat for Rogers the Musical. They pay a premium for a meal and then line up and wait for hours to get a good seat for Fantasmic or WOC.
The congestion is on DLP. If they know they only have 20 good seats, and they allow people to line up early, they should rope them off or create space for others to get around them.
Oh you are so right, DLP is terrible at crowd control when it comes to the hub show. What does help is that there are about 4 shows a day.
For this show there are lines on the ground to indicate for guests where to stand, the red and orange lines. The green dots are the places where the dancers/characters will come by. You have stay behind these lines as during the show. You can stand in the middle, you cannot stand there where there are green dots. Or on the street.
Locals, AP holders, frequent visitors know this. First time guests, do not. And only 5-15 minutes before the show starts, CMs start to move around the people who are standing where they cannot stand. There are always several people who sometimes wait in a place where they cannot stand for half an hour.
By then it is almost impossible to find a decent new place to stand, especially if you are a family with young kids.
For the congestion. The best places for character interaction, are behind the red lines, on the inside of the hub. This will almost guarantee you attention from the characters and dancers. When you are Disneybounding your chances increase. The more often you are standing there, let's say every weekend, the dancers will start to recognize you. If they recognize you, the higher the chance that you will get attention.
You can stand behind the orange lines to get some character/dancer interaction, but chances are a lot less because they run by to get to the stages.
Anyway, in the hours before the show start, the fans stand behind the red lines and sit down (weather permitted)
Meanwhile, day guests will follow the blue line, coming from Main Street, crossing the hub to take a picture and walk towards the castle. Walking through a sitting crowd with a wheelchair or stroller is not easy.
Plus people also want to go from the castle, back to Main Street.
So, they have to look for a little gap between the sitting crowd to get to where you want to be. Yes, usually there is a decent person who will stand up and move back and forth to create a pathway. But it would be much easier if CMs were better at crowd control.