Doesn't this make it take up a bunch of real estate in the header? Or am I misunderstanding you?
I do wonder if sometimes the nested nav is too in-between. Maybe the solution is not to try to squeeze it all into that structure but make "finding the page I want" to be a more top-level experience. EG don't take me to a Category Page, but do let me select a category and start drilling down, whilst keeping it easy to switch between top level categories.
Big nested navs are often just ... fiddly.