On one hand Kant's transcendental idealism seems purely ontological: His noumena/phenomena distinction is essentially a form of dualism. Add to that: Marx considered himself a materialist in opposition to Hegel's idealism.
These two thoughts give me the impression that German idealism was an ontological/metaphysical statement about what the world is made of, not too far removed from Berkeley's subjective idealism.
On the other hand, Hegel's concepts of dialectic and world spirit seem to be more about ways of looking at history, society and the human subject, than any ontological/metaphysical doctrines. We are warned not to take Hegel's weltgeist too literally as some sort of substantial pantheism, but simply as a method for understanding the evolution of human beings and societies.
Is German Idealism an ontological doctrine about the world, in the same league as Berkeley and Plato? Or is it more of "a way of looking at things", a "mere" methodology for understanding humans and humanity?