I don't believe Tesla will lose its advantages.
Every other big auto company has gone to outsourced parts as much as possible. It would take years to undo that.
Every other big auto company would like to go to a skateboard + body approach like Tesla has. A world platform that you can slap different bodies on is the Holy Grail of automotive engineering. They've been trying for decades to do that but ICE's are so intrusive, they can't. Tesla has that with the skateboard.
ICE engine and powertrain design is a money sink. I bet the new variants of the electric motors for the D's and the X's cost an order of magnitude less money to develop than their ICE equivalents. I'm sure the tooling and setup costs are a lot lower too. Then there's clutches, transmissions, etc. Tesla uses software-controlled direct drive and isn't likely to change that.
I could go on but I'll stop here. Basically, Tesla's cost and simplicity advantages come from a combination of: EV, new design methodology, new manufacturing and supply-chain methodology.
The old companies don't believe in EVs and their old methodologies are baked into their corporate culture. With big companies, that kind of corporate culture is almost impossible to change. Worse yet, for now and for quite a few years to come, long-range EVs are viable *only* if you change your basic methodologies around how tightly you integrate the powertrain and battery pack. And have a supercharging network.
So I think Tesla will have the time it needs to grow.
The only question is whether Tesla can successfully sync its growth to the battery tech curve. And if they're going to err, they need to err on the side of growing too slowly. You'd rather be 6-12 months late with the Model 3 than have your company, sales force and service centers tooled up and ready to support Model 3 volumes but have the battery packs be too expensive to make the profit you need.
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The major cause of the troubles at the "big 3" US auto manufacturers was the desire to gain and protect market share- profit was secondary. That is why the UAW will only strike one manufacturer at a time. Market share should not be the ultimate goal, if it is you will forever be producing inferior products and on the verge of failure.
It was worse than that. They wanted to make a profit. But they allowed CAFE to distort their profit/loss calculations. They were willing to break even or even lose some money on small cars if it meant they could sell a high-margin truck or SUV. If you're willing to drop the price enough, you can sell huge number of very mediocre cars. Especially if you own a rental car company that needs to buy new cars every year.
So they spent years getting better at producing mediocre but low-cost cars. And they never realized how outclassed they were because it never showed up on their earnings. Until one day it did. But by then, they'd spent years digging themselves into the hole.