The valuation of Tesla also seems very high to me at first, but given their growth in the other segments such as energy storage and generation, I absolutely think that the valuation could be justified.

Tesla owns the entire vertical from battery cell manufacturing, using those cells to do work (automotive), home and grid energy storage, and solar generation. Throw in the rest of Elon’s companies and you also get the transportation network itself (Boring) and even the data provider for these cars that need to be highly connected (Starlink). And if you really want to believe Elon, some weird, someday a pressurized version of the Cybertruck might become the transportation off of this planet.

And that's not all. They are also now a chip maker, an insurance company, a technology company with some of the leading research and IP in self-driving, and also leaders in automated manufacturing.

Other car manufacturers would be smart to source their batteries from Tesla.

I doubt Tesla will sell to them, Elon has said a few times their vehicle output is constrained by how many battery cells they can make. If they sell those cells to other manufacturers, they won't be able to make so many cars themselves.

Making vehicles is hard. There are a lot of logistical and technological challenges, plus the deep penetration of cars into society means that marketing, perception, and utility are on the lips of the hyper-rich down to the common man.

With batteries... you just make batteries. With cars you have to score adequate or better in lots of different areas to be competitive.