How much of this is a terminology problem—that the word “disability” serves this blanket purpose for statutory reasons rather than to signal the type or severity of impairment?
Like, at the end of the day, these students still have to perform or not. I get the impression that a lot of these accommodations are kind of just a formal way of not being a dick about obstacles tangential to the actual learning.
It's not a major disability but it was a barrier to me performing at my best so I filed the paperwork and got some minor accommodations. It was basic stuff like letting teachers know during periods when I was struggling and they would allow me to take tests in a separate room (same time limit, just by my self in a quiet room) or allow me an extra 24 hours on certain assignments provided I requested it X amount of days ahead of time.
Certainly they provided a minor "advantage" but not substantially. And these were things that most teachers are already generally willing to accommodate regardless of disability but the disability system provides a formal framework for doing so and avoiding the justifying yourself over and over again (vs just getting it cleared up at the start of the semester).
Disabilities come in many shapes and sizes. Most of them are small and it's way easier to deal with an office that deals specially with disabilities to come up with accommodations that make sense for you and keep them consistent across your entire time at university than it does to try and negotiate terms with every single professor or TA.