The rocket equation doesn't participate in capitalism -- moving mass to orbit takes delta-v and that takes fuel.
If you are going to imagine a hypothetical future where starship has made technological leaps forward sufficient to be the cheapest possible option despite being significantly heavier and larger aerodynamically, you have to imagine someone else could also improve their rocket. A smaller rocket requires less fuel to fly.
The US is not the only place flying rockets, and spacex has a lead, but if the industry takes off, there will be other contenders. Once rockets start getting more similar as they all start contending with physics, a smaller rocket will necessarily be cheaper.
If you are going to imagine a hypothetical future where starship has made technological leaps forward sufficient to be the cheapest possible option despite being significantly heavier and larger aerodynamically, you have to imagine someone else could also improve their rocket. A smaller rocket requires less fuel to fly.
The US is not the only place flying rockets, and spacex has a lead, but if the industry takes off, there will be other contenders. Once rockets start getting more similar as they all start contending with physics, a smaller rocket will necessarily be cheaper.