If I had to guess, this was never about convenience and that was just a way for them to put a positive spin on it. It's likely entirely about cutting down on scammers by at least requiring some form of documentation for proof, a pre-arranged effort, and also removing the burden of deciding who gets what accommodations from guest services employees who are not trained in the medical field.
But cutting down on the widespread abuse of the cards is, in the end, a very good thing that benefits everyone, including people who actually need the accommodations. The pass is also good for a year, so overall not that much of a burden for frequent visitors.
I suspect people will complain for a while and eventually just accept it and move on. The same complaints were thrown around 10 years ago when Disney started requiring return times for their disability passes instead of treating them as unlimited Fastpasses. "This is illegal! They're violating the ADA!" Only, they weren't, and eventually the complaints died out.