Not everyone has a hundred companies trying to hire them. They have to take any job they can get to pay their food and electricity and mortgage and health insurance and child support and all that bullshit. And some of those people have PTSD from dogs.
If you create two classes of driver, one who has to follow the ADA and one who doesn't, you've just repealed the ADA.
For that matter, a driver with a severe back problem shouldn't be forced to help a disabled customer with lifting their luggage into the trunk. A different driver should be found. ADA should support both individuals in being safe.
Please note that this suit is not about a person with PTSD being forced to drive a guide dog. It’s about a person who has a guide dog continuously being denied reasonable accommodations.