There's a difference between waiting and waiting for extended periods.
In practice if not in words, the old GAC was the equivalent of unlimited FP.
Even with FP, TSM and Soarin' were perhaps 10 to 20 minute waits.
However, if it was necessary to wait 120 minutes to check out from a grocery store ...
When it comes to airports, I travel a bit and on more than one occasion have interacted with families with children with autism. I've seen a few meltdowns attributable to autism at airports.
As I understand it, autism is a bit like intelligence in the sense that there is a range of abilities. I've been told that some families dealing with severe cases avoid travel, etc. You won't ever see these families at WDW. Others have no problem waiting but absolutely must keep to a routine, hold onto a familiar object, etc. There simply is no "one size fits all" description.
There's a ton of information on the Internet. You might consider researching the topic and see if it answers your question better.
What's clear is that a number of families with children with autism reporting some of the most joyful moments of their child's life are spent at WDW. There is just "something" about WDW that reaches their child like no other place in the world.
It is, after all, "The Place Where Dreams Come True".