Exactly, it only works for the very few.

Accessible cycling is what we need, and that usually means physical separation from cars.

No, because cycling is not for everyone. Multiple modes of transportation should be equally available, but that doesn't mean you should expect that everyone be able to use every mode.

For instance I don't see any particular utility to making infrastructure so that there's enough room for every person to use a motorized wheelchair.

Different conditions demand different solutions.

The point was about, or at least could be made, beyond just cycling.

Replace "Accessible Cycling" with "Accessible form of transport that does not endanger other people not using that form." Whether that's bicycles or wheelchairs or scooters, etc.

The point is that putting them with cars is dangerous.

So what, you want to intentionally exclude people from the benefits of biking? Why? How is that better than making biking accessible to a wide range of people, like some countries already do?