Funny you should mention that. Math has changed so much since I was in school... My ex was taking a business management class, and her math course was having her do some weird shit to say the least, she finally enlisted the help of a husband of one of her hair clients, who happens to be a mathematical engineer, and he couldn't make sense of what the teacher/professor was demanding be done to find the answers. He told my ex that not only is the teacher making things 10 times harder than they need to be, but approximately 25% of the time the conclusions to the problems were not completely accurate the way the teacher wanted them done (Margin of error). He said "common core" is dumbing down people who use it.
As I read your second sentence I hit the Reply button to say that teaching math is what changed not math itself. Then I read the rest of your post which is spot on but I'll still finish this post with math in schools is all about the so-called educators feelings not facts like math.