Retro-propulsive landing of an orbital class booster has not been ever demonstrated. Falcon 9 First Stage is the only booster that ever existed able to do it. The full-flow staged combustion rocket engine is also a new technology that will fly for the first time in Super Heavy Starship. Rocket science is literally a synonym with "difficult".

Here you have how SpaceX looked like in 2002: https://i.redd.it/00ikcxo2z0f01.jpg

My guess is that in 20 years people will be also saying how he took an existing technology and sold it to a mass audience.