A complex system that works is invariably found to have evolved from a simple system that worked. A complex system designed from scratch never works and cannot be patched up to make it work. You have to start over with a working simple system.
General systemantics: How Systems Really Work and How They Fail, 1975, John Gall.
Gall's law warns about traditional approaches to solve complex problems, by doing a holistic analysis and design to later move to the implementation of that design. In Gall's opinion this course of action is deemed to failure.
The iterative approach of building sprint after sprint increasing functionality on each delivery would be a better suited procedure.