Plenty of programmers don't work at a reasonable standard; See, for example, every security incident ever, proliferation of slow electron apps, commercial software that flat-out doesn't work properly.
However the standard for performance is relative to reasonable expectations for someone in that role. Typically relative to peers within the company. If one person is unable to do their job to within a reasonable level relative their peers even with reasonable accommodations, accommodations do not require the company to continue employing them anyway.