That would seem to be assuming that their investments are required and not optional. After all, they have nearly a half-billion in the bank. Holding onto it would say that there is no investment in the business they can make that returns better ROI than the ~2% they'd get from keeping the money in the long term cash equivalent investments.They loose money.
Look at the cash flow. Also, look at cash levels - capital actions.
As a mature company trying to maintain a product line but not expecting rapid growth in products, perhaps that might be true. You're doing the normal R&D every year to replace the models you currently have, and you're expecting growth rates in the 5-10% range. But as a company trying to grow their product line (1 car -> 2 cars right now, 3 cars later), and looking for growth rates more in the 50-100% range, I would expect them to be spending money on R&D faster than it's coming in.
Another investment they're making is in the supercharger network. The number of superchargers they need is going to be a function of the number of cars the sell, and it looks like they're trying to get ahead of that curve right now... but perhaps if you worked at it you could make a case that the costs of the superchargers bring down the margin of the cars to an unsustainable level. That would be a more valid case to make than "They're investing the money they have to grow the business, and therefore they must not have a valid business", which is the case you're currently making.