I find the point that SpaceX has no plans beyond the next step hard to believe. I could imagine they perhaps have no firmly officially approved plans like a full waterfall project, but surely there must be already a lot of trade studies on the next steps, and at least some rough plans.

Or maybe the even have approved plans, but with the understanding that they could change quickly as new data comes in.

Otherwise a project like StarShip is likely not feasible. For example for a Mars project you must at least have some idea that long term live support is feasible with the chosen size. They likely have that idea based on data from ISS, but I bet there were some preliminary studies on this at least.