Tesla started as a supercar company and slowly migrated to what it is today. Electric tech was actually old by the time Elon started, with GM already having built the EV1 program. This was all proven technology waiting for the right group to monetize. It also helps that lithium ion pricing had fallen significantly. The EV1's biggest fault was its old school lead-acid batteries which couldn't deliver the range and power li-ion could. In hindsight, li-ion and electric cars are a no brainer. That combination with, lets not forget, Tesla's and its buyers vast government subsidies turned out to be workable.
SpaceX for all its wonders, exists only because of the COTS program generously funded by the US taxpayer. Its been a long slog to its current levels and still has a way to go, but it has customers and accomplishments to show for itself and builds off rocket technologies that are decades old. Both of Elon's businesses are more refinements of existing technology than pie-in-the-sky daydreaming.
That's very different than giving speeches and interviews about living forever, having a 2001 style AI in your home, and airports run by robots. Musk is still in his peak. I guess we'll see how he turns out, but he's not comparable to Page yet.
Elon Musk doesn't want to rule the Earth.
He wants to rule Mars.
That doesn't really speak to him being a closet authoritarian or anything, though.
Everything I've read about the man makes me think if you gave him $100b he would invest all $100b in doing some awesome project which would only be successful through the superhuman efforts of himself and his team, but wouldn't require a command economy otherwise. Vertical integration inside, yes.