Did they?

No, no rocketry expert ever said that reusable rockets were impossible. They would have told you that the cost to develop them would not recoup itself based on the then-existing demand for orbital payloads, and that banking on such demand materializing would be a massive gamble (which is why Starlink exists).

Falcon 9 is partial reusable, took a lot of money to do so and yeah its a good product. Not sure how expensive it was for US americans to gift it to Spacex but sure.

The highest number though is like 30 uses and Starship still hasn't profen itself.

Also the boring company, Doge, Solar City, the cybertruck etc.

So what do we get out of this? Musk is for sure not just an idiot, he for sure sees sometimes good opportunities, but also he had the money to invest in these and he got lucky a few times too.

Btw. the cybertruck he announced, never came.