I think you make a mistake in assuming that a child can only learn what the parents can teach. Especially when you consider that our society calls us "children" even up to age 18 or 21, many years beyond the traditional coming of age at 13 or 14.
I'm not homeschooling yet, but have been researching it for some time and may start next year. A heck of a lot of the methodologies that I'm learning about have parents acting as "facilitators" more than teachers. Especially at the middle and high school ages, kids should be able to pick their own books to read, carry out projects, learn skills by self-teaching or by seeking out lessons, etc. The parents' job is to teach the children how to think and how to learn (and even in that regard there are resources to help).
I'm not homeschooling yet, but have been researching it for some time and may start next year. A heck of a lot of the methodologies that I'm learning about have parents acting as "facilitators" more than teachers. Especially at the middle and high school ages, kids should be able to pick their own books to read, carry out projects, learn skills by self-teaching or by seeking out lessons, etc. The parents' job is to teach the children how to think and how to learn (and even in that regard there are resources to help).