Not all outline views are table views, however, all table views are outline views, therefore outline view should be higher the the hierarchy.
Well, it is! You are just seeing it wrong. NSObject is the core, all objects descend from this object. From then on all other objects are at a higher level from NSObject.
Sure NSObject has basic functionality for numbers and strings, but not for more complex things like OpenGL, movies, ... That's why an NSOpenGLView for example is a subclass of NSObject, but is at much higher level than NSObject.
If you're looking at a tree hierarchy of all the classes in Cocoa, you will see NSObject at the top of the tree (which is the root). This means however, that the root is the lowest level in the hierarchy. Just like the root of a tree in real life.
Your idea of a subclass is not the general idea.