The geometry Fusion 360 generative design can produce is largely dependant on the manufacturing method- selected by the user. This is so a design that is produced by the software can actually be made into a real product.
Original 
Unrestricted geometry 
Additive Manufacturing
The difference in geometric complexity between the unrestricted geometry (middle) and additive manufacturing (right) solution can be seen. This is because additive manufacturing (3D printing) is still limited by the geometry it can produce, but it is far more capable than other manufacturing methods, such as casting.