I think SpaceX is taking the re-usability part of Starship as foundation. Meaning they won't move forward until it's solved. With Falcon they added it as a bit of a secondary priority. They've spent so much resources trying to get the second stage back to earth. I think they should have just focused on getting the whole system flying to orbit, throwing away second stage for now, and using that platform to replace falcon. Eventually, they could refactor second stage to get it back to earth. But perhaps it's all too coupled that it has to be solved at one time (not later).