I think you misread my comment. I'm specifically
not advocating for different treatment. I'm saying any employee who wants to use the bathroom six times a day should be permitted to do so, IBS or no IBS. If you want to enjoy the ambiance of the bathroom six times a day, that's fine.
So, Amazon can easily write up neither employee, which means they don't need anything to justify the different treatment.
(Also, no, Amazon can write up one employee and another just fine. They're an independent company in a free country. They don't answer to Lord Business who tells them they have to run their business a certain way. They can do whatever they like, provided they don't run afoul of a few laws like Title VII or the ADA. And all that will happen if they do run afoul of those laws is they'll get sued - which is exactly what happened under their current policies, so....)