And it seems like other manufacturers, even if they make good EVs, won't be able to scale their battery production quick enough. Meanwhile Tesla is quite ahead in this department.
Their expressed goal is actually closer to 20M vehicles long term. That would be on top of their plans in the energy sector (batteries, virtual power plants, etc.). And on top to eventually have a cheap, driver less car on the road. That last one is a bit of a controversial goal and you may have some reservations about whether they can or cannot do that. But if you are an investor you might reasonably lean one way or another and buy accordingly.
If you look just at their current size and assume they cannot possibly do more and grow, then yes, you'd be right to be skeptical. If on the other hand you look at what they did with quarter on quarter growth (until the current one), and extrapolate that some years in the future you might start wondering where that might end up and you might see a path to Tesla becoming quite big indeed.
The reason the share price is high is obviously that there are a lot of share holders that believe that Tesla is well on their way executing the necessary steps to reach all of their ambitious goals. They seem to have a head start on other manufacturers both in volume production and cost savings. That won't last forever. But at the scale of Tesla's ambition, having a lot of control over their suppliers and R&D related to that is a smart strategy if you plan to grow aggressively and something that most of their competitors are still figuring out. Maybe some of them will and maybe some of them will have to sell products at a loss for some time to come just to keep up.
IMHO, the biggest threat for Tesla are not European or US companies but Chinese manufacturers. The market is plenty big enough for the both of them though. It will be interesting which of the ICE car manufacturers survive this decade.