Almost any product that is built without input from the people who are going to use it is going to be inherently worse. Imagine a team creating a camera from scratch who are not photographers, and who never included any photographers in the design process. It would be a functioning camera, I’m sure, but it’s usability for real-world use would almost certainly be worse than those developed by teams that include professional photographers.

The effect may be less for accessibility features, but it would still be there. I’d highly suggest anyone building out accessibility features to at least consult with disability advocates and other end users.