That's an interesting take, but it's not borne out from the people I've met. Often they do have gaps in knowledge, but reading and writing definitely aren't the problem. Most of the unschooled people I've met have had a broad knowledge base with gaps in specific areas (admittedly, most commonly math or science).

But they've all been able to learn when faced with a problem. Most learning up to high school is pretty decidedly useless. Most high school subjects, like math, are taught very inefficiently and a student can catch up.

Beyond that, community college transfers to prestigious universities are common. The most important piece is the ability to learn and understanding that not knowing specific subjects will be limiting in the long run.

Not sure about now, but 20 years ago all it took to get into the in-state university system was SAT scores and a GED.

Transferring from there to other schools in the US was pretty straightforward and there weren't any application essays until grad school.