The teacher is not up in the middle of the night with the child when they have strep throat. The teacher is not up in the middle of the night when their child has a nightmare. These are the sorts of things that only happen when you are a parent.
I understand your what you're saying, but this argument works against the argument that parents are automatically qualified by virtue of experience: a mother of a 2-year-old has no experience raising a 3-year-old either.
A childless teacher is a pseudo-parent 8-3:30, 5 days a week, 9 months a year. They honestly havent got a clue. They can head home and chill. While parenting is an endless grind.
Kids will wedge into every spare moment and literally consume all the space, physical and mental energy.
Try spending all night up with 3 kids with the stomach flu then having your boss push you to meet a deadline the next day.
These teachers, including my mother in-law can keep their `advice`.
Experience did not make me a better programmer or mathematician. Diving deep into the details to get a much better knowledge did.
Update typo
In fact, I'm actually skeptical about the effect of parenting in general, versus the influence of genetics.