Does SpaceX have any investors other than Musk? I thought he bootstrapped it.

You can't know anything for certain but most of every analysis corroborates what they themselves say - they're operating at a healthy (though thin) margin on rocket launches and printing money with Starlink.

The context of this of course is that they've sent the cost of rocket launches from ~$2 billion per launch during the Space Shuttle era, to $0.07 billion per launch today. And the goal of Starship is to chop another order of magnitude or two off that price. By contrast SLS (Boeing/NASA's "new" rocket) was estimated to end up costing around $4.1 billion per launch.

Most of their income comes from government subsidies and grants. So, it is rather funny to see the owner of the company running around the government and "cutting" costs.

If they can keep raising money from investors, that seems proof enough to me that the economics must be good enough.

Ie investors would only put up with losing money (and keep putting up money), if they are fairly convinced that the long run looks pretty rosy.

Given that we know that SpaceX can tap enough capital, the uglier the present day cashflow, the rosier the future must look like (so that the investors still like them, which we know they do).

They undercut every other launch provider. There's no way they're burning investor money to achieve that at the scale of their operations. This is all due to the cost savings of reusable F9. If they wanted to they could jack up their rates and still retain customers and still be the cheapest. There is no reason to believe they are unprofitable.

The economics very likely didn’t work. It’d be irresponsible for a launch company to model Starlink without a customer knocking on your door with a trailer full of dollars to sponsor the initial r&d and another bus of lawyers signing long term commitments. Vertical integration makes the business case much more appealing.