> These points are all so well-reasoned and difficult to argue against, I can't fathom how they managed to get all the way to this point without these things coming up and causing a rethink of the base approach. Quite incredible.

Isn't "launch from a plane" basically reusable first stage, 1.0? It was also more conservative, since the idea had already been successfully implemented in 1990: https://en.wikipedia.org/wiki/Northrop_Grumman_Pegasus.

Some quick googling shows Virgin Orbit started in 2011, and SpaceX landed their first rocket in 2015. Virgin Orbit's idea may have make a lot more sense before SpaceX proved out an alternative, and that didn't happen until maybe they'd done a lot of development that could have possibly paid off.