Given empirical practice and the business model of the company, the employer's two documented lists of essential qualifications for the job suffice to deny the ADA claim. Even if the employee were to delegate those tasks, it would amount is substantial enough that it would amount to a delegation of the job itself.
Since 2011. An occasional commonplacing of the U.S. Circuit Courts of Appeal.
Neither an authoritative statement of the law nor legal advice. Quick work.