I don't think you've thought any of this through...
When you work in a senior system... protecting that is huge. Also, protecting the roles and who can do what is not trivial. Imagine if Disney laid all the people off and then tried to have a smaller group of people do 'many tasks'. I'm sure the unions ensured that only the correct role could do a task.. not a scab. This ensures the union people will do the essential jobs.. with the right people. The people having their benefits and not being forced to pay COBRA are going to disagree with you a lot as well. In addition, by staying in the union, Disney's decision to lay people off in the future still goes through the union.