Untrue. Any teacher must be familiar with both the subject matter and basic pedagogy, regardless of whether they're teaching one student or many. Yes, there are additional skills necessary when teaching a larger class, but I think you drastically exaggerate how much of a teacher's job that is.
People put a lot of stock in the intelligence of teachers, but consider it this way, most teachers choose a career that requires a 4 year degree plus certification that won't make enough to live comfortably or earn them over what a standard retail job makes much less pay their loans, this is something they think long and hard on (which is probably not much more than "I really like working with children") and make their decision on. It attracts the kind of people who think that's a good idea. Anyone more intelligent that wants to teach runs the numbers and decides against it except in rare cases. Any pedogogy those kinds of people learn isn't that advanced and can be picked up by most by reading a book on it over a month. These "professional" educators isn't exactly an advanced profession like that of a medical professional or a scientist, most of those people would struggle or fail out of such programs. The alternatives for most teachers is a communications degree, or sports/massage therapy. Altruism doesn't equate to being good at something, the proof is in the quality of education offered today.
Edit: They don't deserve contempt, but I'm saying if you increased teacher's salaries, the competition would be such the people that go for it now would simply unable to compete with the sudden competition based the altruistic motives plus pay. Altrustism only motivates you so much, doesn't last long when you're over worked and under paid and dealing with 30+ class sizes. Pedogogy be damned, you'd get people who would be able to actually teach kids on an individual level and demand more from administrators or have the conviction to walk out and move on to something else if they didn't.
Yeah, I know, it's not a "rational" choice by Randian standards. To some, that means they deserve contempt. To me, it suggests that they have other motivations that might deserve some respect.
I think you are imagining a homeschool from the 1980s. My kids learn many aspects of the subject matter from sources like Khan Academy and Outschooling. The idea that the teacher needs to know the subject matter deeply in order to manage the child's education is obsolete.
If those allow you to outsource the entirety of your child's education, including personalization of the curriculum to individual needs, answering arbitrarily-deep questions about the subject matter, etc. then great, but I'm not sure I'd call that home schooling. That would be more like a (virtual) private school, with the same level of parental involvement. If you want to be more involved you need more training, simple as that, and the fact is that a lot of home-school parents don't even have an average education themselves.
Also remember, you're not the sample. You claim to have some expertise in data science. What do the data suggest, for a typical home-schooler and not just for you or the non-random sample of others in your neighborhood.
Seriously, consider what you’re saying. You’re saying that people without an education in pedagogy are unable to teach. Most of the parents reading this probably taught their children how to read before they got to school. The overwhelming majority of college faculty never have any training in teaching. Many, many people tutor without ever getting an M.Ed.
You get better at teaching by teaching, same way you get better at painting by painting or playing music by playing music. You’ll get better faster if you’re paying closer attention to your students and what you’re doing and things like having someone watch your lessons and critique them or reviewing video of your lessons yourself afterwards helps enormously. If you want to be play violin an encyclopaedic grasp of music theory is less useful than another hundred hours playing until you get over 1,000 hours at minimum. Ed school lecturers and professors are not noted for their excellent teaching despite their presumably excellent grasp of theory.
My experience could be unusual, obviously, but what’s very unlikely to be wrong is the literature on the determinants of teacher quality which does not reliably find any effect distinguishable from zero for teacher training or for experience over six years.