A line (to me) is defined as two or more points that connect.
And to your second “point”, how is learning to do the math, rather than just memorizing a list of answers, “directly involved in what we do as an adult”?
The heuristics are what is valuable - the ability to look at a problem, break it into smaller chunks, and the select the correct algorithm to process that smaller chunk.
Eg, cleaning my apartment: I divide the apartment into sections (bathroom, living room, kitchen, etc), then apply the correct cleaning algorithm to each room.
It’s the higher order thinking skills that really matter, and those are trained and exercised in math classes.
In my practical pedagogy, I try to emphasize heuristics more than algorithms or “facts.” My goals vary by student, but there are good higher order thinking patterns that can be taught with any math concept.
I agree with you that math education is messed up. The way to fix sequencing is to align it to the science sequence, ideally teach it simultaneously. Partial credit for common error categories, based on work shown. I’ve become the evil math teacher that docks points for not including units in geometry (I promise I say it like forty times while they are testing!) because I want them to connect what the math is saying to eat it would look like.