Much of what is taught in teacher training is specific to the classroom environment and is irrelevant to home education. In fact, teachers-turned-home-educators often report that their teaching experience is more of a hindrance than a help. They discover that in this new landscape, they must let go of their assumptions about how children learn and take a fresh look.
Group instruction at school is inefficient from the point of view of the learner. What is being taught in any given moment may be too difficult, too easy, or not engaging to that child. So they tune out, and the teacher has to work extra hard to reach them. One hardworking teacher is trying to achieve this engagement with dozens of children with different needs all at once. It's a very tall order. Of course, some of the children won't behave as desired - from boredom or other reasons - so the teacher has to deal with those behavioural challenges, while still trying to engage all the other kids. I agree with you, OP: teaching is an incredibly tough job.
Compared with that, what I do is a walk in the park. I know my own children well. Everything they learn is at the right level for them. If they aren't interested at that moment, we do it later when they are interested. We aren't stuck with a particular book or approach. If the material doesn't excite them, we change it for something which does.
It's possible to put yourself in the role of facilitator of your children's learning, rather than "teacher". In this case you don't have to know things which you impart to your children. Instead, you help them find resources to educate themselves. Those resources can include books, videos, toys, equipment, websites, and other people.
My two are now 21 and 15. They've learned under their own steam in an entirely different way to how children are taught at school. At no point have I felt like a teacher. I admit that I did harbor a secret hope that the eldest might want me to teach them maths, since I have a maths degree and love the subject. But no. In the runup to maths GCSE they came to me maybe once or twice a month with some question they could just as easily have asked someone else. They pocketed their respectable maths result and spent most of their time on their main interest, which was art. That one is now getting on brilliantly at uni, having already learned how to do research, ask the right questions, and work in teams. These were all skills picked up in the extra time which was freed up by the more efficient approach to learning.
The younger one has a learning disability and has been able to learn at the right pace for her, without inappropriate pressure to attempt to do what the average child of her age can do. She won't be sitting exams at 16. I expect she'll do qualifications of some sort later on. Meanwhile, she is learning life skills as well as academics. In keeping with her developmental stage, she is also spending a large amount of her time playing!