You're correct, we don't have evidence that SpaceX is pricing below cost, because we have no idea what Falcon 9 launches actually cost, because SpaceX refuses to tell us.
SpaceX has shown these numbers to investors and have received money on good valuation. If not even there core buissness was profitable why would anybody invest in Starship?
The argument that SpaceX subsudizes their launch prices is just a nonsense argument that doesnt hold up to study.