I wonder how Husserl's solution to the problem of psychologism compares to Muller's 0-D theory. The structures are instruments we create, and which have limited, never comprehensive, validity. Husserl's metaphysics was, it seems, a relapse into mind-independent reality. A 'transcendental ego' could in principle be used as a working structure, but the term was apparently meant to be ontological, and in my opinion static ontology and also static idealism are unhelpful and should be avoided. No one operates or can operate without mental structures.
Mental illness means among other things functional insufficiency of some structures.
If all of mind is a set of structures constructed by unknown principles, none of it, and nothing at all, can have any intrinsic meaning or value. Structures come and structures go. Some structures confer meaning on other structures, but only by structural convention. Some are considered more true or more real than others, but only by convention. And this not only on a conceptual but also on a pre-conceptual level, elaborating for instance with the help of biologically determined structures.