Obviously, I'm missing something.

The right way depends on how much display information your GeoJSON contains.

If it contains up to 1000 points, you can use Drawing API.
Example:
https://infinity-code.com/atlas/online- … ample.html

If it contains more information you are better off rasterising your data, split this into tiles and use it as an overlay.
Example:
https://forum.infinity-code.com/viewtopic.php?id=1478

Basically, I have GeoJSON data defining the boundaries of some land. I'm able to convert this to an array of Vector2's to create a polygon of the lat/lon pairs that define the property, but I haven't been able to figure out how to draw them precisely on the map (I'm using Google Maps "Relief" if that makes a difference).

Accuracy is important because at the end of the day I have to hand it all over to an architect.

Oh, and I'll need to be able to zoom and rotate them along with the map, because some parcels are in LA, some are in Seattle, and some are just plain random houses...

Any examples I can follow?

Thanks in advance.