>Startup founders are generally leveraged on the upside but not on the down.

I don't agree with this at all. This assumes zero costs on the part of the founder when it comes to a startup. There are significant costs, including extra work, low or no salary, and opportunity costs.

I agree that the potential upside is much more like a call than a long position, but all calls have a premium cost, and have a much higher risk of being out the premium cost with no reward.