Get a landscape or regular architect's opinion? Our regular architect figured a way to 'level out' a former porch, planter and 'jazzed up' greenhouse. There was varying thicknesses of concrete, a recent channel for some interesting plumbing, loose bricks (tightly laid over rock and dirt) and one square old slab six inches under those bricks.
I know that all sounds wacko but I'll eventually post pics of the project here and if you haven't fixed it by then it could help you think outside the box.
Current state:
Not awake enough to delete duplicate pic....