I apologize; I know nothing about ARkit - but a couple of things:
you'll need to look at the docs to see exactly what space 'projectPoint' projects world space into to. Is it projecting points to some kind of normalized device coordinates? (NDC's typically have a range of -1 to 1) Or is it projecting points to some kind of device coordinates (to which it would need to know the device parameters - size and shape). Or, is it projecting points to some kind of eye coordinate system? You'll need to look at the docs to know
what the heck are you doing with setting up each feature points? You're using the x and y coordinates of the projected point, but the z coordinate is a world space distance - presumably the distance from the camera to each UNprojected point. From strictly a 'visualization' point of view, that doesn't make a whole lot of sense. Are you using the z coordinate when trying to plot the feature points?
Plot them in Python 'on top of the frame'? That doesn't say a lot. When you plot something, you tell the tool 'how to plot' - i.e., where the origin is, the scale of the axis, etc, etc.
