Maybe the market's valuation is a lot of people betting on Tesla being able to scale up dramatically in a pace that current car manufacturers will not be able to catch up with. Not entirely unthinkable.
We're in the middle of a turning point in the car industry. I'd wager in 2-3 years sales of electric cars will already be a sizeable chunk of the market. Within about a decade electric personal cars will take over sales of petrol cars. But nothing suggests that VW, Toyota etc. would not be any less apt at producing electric cars than Tesla. On the contrary, the established players have a MASSIVELY superior pre-existing production capacity and expertise.
[1]: https://www.reuters.com/article/us-tesla-batteryday-producti...
They need batteries for those cars. Are they also investing in battery production?
The form has not standardized, they evolve quickly, they can not be purchased in the volume required by all producers, and a better battery and matching charging infrastructure is a major competitive differentiating factor among EV manufacturers.
Tesla is not without its problems, but I think it's a bit naive to focus on the solved problems as limiting their potential. It's also the wrong thing to look at - Tesla is concerned about dictating the future of transportation and energy, selling cars is a means to an end.
It is definitely true that the US market cap has become "decoupled" from its current economic output, but as you say, that is a (rationalised) prediction about the state of affairs in the next year or three, it's not "oh no everything is cer-aazy!"