Actual real world right now giant rockets include

• One that is being built under waterfall methodology. It has been being built for several years. That’s the Blue Origin New Glen heavy lift reusable rocket

• One that is being developed under an agile methodology, it flew as a subscale lander to test their engine and flight control, it has flown four full test flights, improving on each. That’s SpaceX’s Starship

We are yet to see either launch a payload to orbit