> but that's just going to take a long time, particularly if F9 is, say, sub-$15m per launch.

1) SpaceX isn't a public company; among other benefits, there's substantially less pressure to maximize profits.

2) Starship launch costs don't need to compete with F9, they only need to compete with the other competition.

Also, it's worth repeating that the goal of this entire endeavor is reaching Mars. The above state of affairs isn't a coincidence, but a very deliberate part of Musk's plan. (Also, luck.)