Disability accommodations, including DAS, as there to ensure access; they are not there to make up for the hardships of everyday life, and they are not there to get more done in less time because someone can't spend a full day in the park. They're there to provide access, period.
if everyone with a valid disability were given a DAS, it would negatively impact every other guest in the park, including other disabled guests. Disney has a right, no, a responsibility, to avoid that outcome. They've chosen to limit DAS based on issues caused by the line rather than issues that might occur in the line.
A line had to be drawn, and I think Disney got it right. My hope is that they don't back down, and continue to hold the line.