They can significantly grow with declining market share if the market for electric cars itself grows significantly. That market is currently < 1% of all cars sold.
They did all right.
I’m not a huge Tesla fan, but the idea that they might become an enormously profitable company without turning into one of those conglomerates that sells cars at every price point seems reasonable, especially in an age where the margins will be in tech and services rather than in selling steel bent into the shape of a car.