>I suspect that the alignments we see - quite plainly - are the result of us just beginning to learn about geometry then

Not sure if I agree with that one. Humans must have been aware of simple geometry for countless millennia. If you drop something heavy it falls in a straight line, we see in straight lines, we walk in a generally straight line, most trees tend to grow straight, etc etc.
If you want to make an arrow or spear you soon learn what shape to make it…

If you put three or more straight objects together then you’re into polygon territory.

I think we tend to underestimate these ‘ancients’ as if somehow there was no knowledge prior to the Neolithic – obviously not true, we just have very little hard evidence.

I do have to agree with what you say about metals though, these early shiny objects conjured out of rock and fire by people with ‘the knowledge’ must have been awe inspiring.

-Chris