It sounds like you'd be incredibly useful for the spirit of accessibility, but need to work on your knowledge of the rules of accessibility. When we build accessible applications at our company, we have to comply with every rule of "WCAG AA 2.1" to satisfy our clients.

A professional audit of our product would result in a report of exactly which rules we need to address, along with suggestions for possible changes. I would use this to satisfy the accessibility portion of our contracts. So an accessibility expert is, among other things, a compliance officer who provides credible proof that a company is actively respecting the ADA.