I went through a normal school system (the first 8 years still during the communist regime in my country, so take that "normal" with a grain of salt), and the gaps in my knowledge are enormous, in some cases subject-wide. I know literally nothing about chemistry, except the bits you learn here and there from TV shows and such. I vaguely remember some kind of equations, but nothing stuck. Biology - everything I know I know from somewhere else, mostly from that TV show with talking blood cells [1]. Surprisingly, I had pretty good grades, but it had nothing to do with knowledge - I was able to quickly scan the textbook before an exam and somehow it was sufficient, but there was no retention, I forgot everything after the exam. I was forced to learn Russian for 4 years and I remember literally nothing, not even the alphabet.

Those are mostly just anecdotes - I am sure that modern schooling can do better than rote memorization in a toxic environment. What I want to say is that motivation, a friendly environment, and fun learning are a lot more important than how well the teacher knows, say, chemistry. It is entirely possible that your kids will retain more knowledge, not less.

I am only talking about elementary school, college was different - I loved it and learned a lot.

[1] Il était une fois... la vie - https://www.imdb.com/title/tt0284735/