Its only a false simplicity if you still need to track the interaction between everything and everything else.

When you break up a problem the goal is to find clear bottlenecks of complexity such that you can abstract a thing to its inputs and outputs and ignore the complexity within. You reduce the amount of knowledge required from any given perspective, thus reducing peak cognitive load.

Sure the system is as or possibly slightly more complex, but there is a distinct advantage to reducing the peak complexity of any given sub-problem.