If we're really digging into it, the actual value of a company should be the amount of money you need in total to buy it. Including the parts that are not for sale (so not just the public shares)

That also means for instance convincing the US gov to let you have Tesla, and vice versa convincing the Japanese government and all Toyota's debt holders to not intervene in case of a Toyota buyout.

And that becomes a completely different story with undefinable numbers and so much more politics.