[Gravityloss]

SpaceX did some good standard mainstream solutions. Sometimes success is not about some exotic innovation but doing your normal job well. A standard lox kerosene gas generator rocket engine. Flat aluminum panel construction. Only the interstage is composite. Started small with Falcon 1. The Merlin engine had heritage from NASA's FASTRAC program.

If you look at Ariane V, Atlas V or Delta IV, they all have some peculiarities and operational warts. Large solid rockets, Russian engine, hydrogen. In some sense, Falcon 9 is the most "ordinary" of the launchers available now.