Tesla is already publically traded. It's valuation depends on investors buying into Musks vision.

As a rule, investors optimize for long term growth since that's what maximizes valuations. All the megacap companies are judged by future growth.

The effect is companies tend to exaggerate and lie about what they can achieve in the long term to juice their own stock. Elon's def got the juice.

Investors should optimize for long term growth, yes. The problem is Management (CEO, etc.) will get fired if things look bad. So the incentive for management, if they can get fired, is to ensure monotonic increase. Sometimes — especially for a rocket company! — you should be allowed to fail for a few years. You should be allowed to take big swings, without risk of getting fired. If Elon knows he is in control, he can think long-term. If he's at risk of being let go if things look bleak, his optimization function will be different (and, IMO, net worse for society).