It's a bit more difficult than that. The FSC is highly resilient and adaptive, hence the "Super Cell". It is essentially a blank slate that changes and adapts to whatever situation it needs to fit into. This is also why the Pure Forms, entirely composed of FSCs, have the ability to change their shape and form so fast. While the Forerunners called them the Flood, do not forget the ancient humans called them the Shaping Sickness for a reason.