> What's the average selling price of the BMW 5 versus the Tesla S?
The average price doesn't matter. The actual price matters and this differs from country to country to such an extent that it will be a large factor in the decision making process. For 2017 NL and Norway for instance were big sellers for Tesla because of huge tax breaks on purchase and subsequent ownership taxes.
> The BMW 5 appears to be significantly cheaper.
In NL they start at 56K Euros, the Tesla's at 90K+, but the tax situation is so convoluted that you can't even compare the two at that price point. Which is why you'll see plenty of Tesla's in lease fleets because the monthly figures on that very expensive car compare favorable with the 5 series.
> Besides that, Tesla is growing rapidly, BMW is not growing at all.
Yes, this is usually the case when companies start out. BMW is just over a century old, if they would be growing at the rate of Tesla they'd be the only manufacturer by now. Just like any new company Tesla will - hopefully - continue to grow for quite a few years but it is my expectation that that growth will plateau at some point in the next couple of years.
> In the US, which is a massive market for BMW, they're contracting.
See above for comparison between mature market players and start-ups. This is expected, there is a new equilibrium to be found and all existing market players will lose some market to a newcomer operating in their segment.
If that would not happen it would indicate that the market as a whole is growing which is not the main driver here.
> So when it's 30k S vehicles in Europe next year, it's just going to hurt that much more if you're BMW.
No, you have to divide that over all the competing vehicle brands to figure out how much it affects them. And even though the 30K vehicles sold is impressive it's for now not at the level that the likes of BMW and MB are having end-times nightmares.
> The car market in the US and Europe is not meaningfully expanding, every Tesla sold is coming directly out of the pocket of BMW, Mercedes, et al.
Exactly. But until those numbers reach 100's of thousands of vehicles sold Tesla will be the underdog, and by that point the likes of BMW and MB (and possibly VW) will have a competing product. There is no way that Tesla will be able to absorb the whole car industry without the competition putting up a stiff fight, the way it is playing out right now is that Tesla is taking all the risks and laying the groundwork for electric car acceptance and infrastructure issues. It's a real world example of the innovators dilemma at work and it remains to be seen if the incumbents wake up in time to win that fight.
> The ~120,000 Teslas that get sold in 2018 are coming directly at the expense of the German automakers.
No, they are coming at the expense of all automakers, maybe with a larger chunk coming out of the German automakers but that's not something that you can say without more proof than I have available right now, what I do know is that both the E class and the 5 series set records in the US in 2017, with both cars individually growing in sales as much as the total number of sales for the Model S.