I'm a novice learning about Arcade.
From my limited experience, it seems like there is a hierarchical nature to Arcade types and subtypes.
If that’s correct, what does the hierarchical structure of geometry types look like?
Also, are the types considered to be object oriented?
Are the types considered to be object oriented?
No idea how the types are implemented behind the scene, but if you take a basic interpretation of "object oriented" as
For Arcade, similar to the question about arcpy that you linked, the class hirarchy (the "IS A" relationship) would be
Geometry would define the common attributes (type, hasZ, hasM, spatialReference), while the types define their own special attributes. Note that you can't use a Geometry object, but only the distinct types.
I wouldn't consider the rings and paths attributes to be part of the class hirarchy. They are components of their respective types, implementing a "HAS A" relationship (e.g. a Polyline has an array of arrays of points).