I've said this before in this thread, multiple times as a matter of fact. Pre-IBCCES, my father was approved for GAP passes, based on documentation. What documentation? Reports from multiple doctors including specialists, along with MRIs, physical therapy reports, and post-procedure reports from several different medical procedures. Who approved it? Universal's disability manager. What was the role of the front-line Guest Services employees? To look up his GC code in the computer, see that said disability manager had approved that specific accommodation, and print out the passes. How did he know to ask for it? He tried the AAP. It didn't work for him. He went to Guest Services and explained that it didn't work and why. They told him there was a higher-level accommodation available, but that because it was considered "better" rather than "equal" access, he would have to provide medical documentation. He said OK. They gave him a phone number to reach the disability manager (or more likely his team, it was a few years ago, I don't remember exactly who he talked to). They explained exactly what he would need to submit, where to send it, and how long it would take to get a decision. When the decision was made, they called him back with a GC code and explained what to do to get the passes each time.
It's not an insurmountable obstacle. It's not undefinable. It's just something that, like most things involving a disability, requires time and effort. Is that "fair"? IDK, and it's not really up to me to say. Theme parks are free to set whatever standards they want, as long as they meet the minimums required by the ADA.
ETA: My dad isn't someone special who magically knows all the ins and outs of the process. We've met several people over the years who were also approved for GAP passes through exactly the same process. They managed to figure it out too.