> if a person is visually impaired, why wouldn't they have tools at their disposal to make things readable?

If it's on a screen in a browser, probably. If it's printed, or on a display not under a reader's control, probably not.

FWIW, I'm partially split. I generally prefer sans-serif overall - have for decades. I think I slightly prefer serif for some printed material visually, but... when I actually have to engage and read it, for long periods, I think I tend to opt for sans-serif. Noticed this on my kindle years ago, and kindle reader now - I usually swap to sans-serif options (I think it's been my default for a while).