> The innovation here isn't about reusability at all, it's about the economics of reuse.

It's about both.

SpaceX showed that the 1st stage of a rocket can be reliably reused in production. Which is really important from an architecture perspective because 2/3 stage rockets are just more efficient than 1/1.5 stage rockets (mostly due to the propellant mass fraction term of the rocket equation).

To give some examples, the payload mass fraction of some reusable rockets is:

* Shuttle(partial reuse): 1%

* Falcon 9(partial reuse): 4%

* Starship(full reuse, in development): 2%