In your altered (before it was a race driver?) car rental company analogy,

Nope, was always a rental car company analogy.

the developer would be the car rental company and Unity the car company? This would mean the developer would rent Unity to its users?

No, a car manufacturer makes the car that would be unity and then sells it to their customers which would be the developers.

Now if a developer was a rental car company, and they rented the car out to their customers, the rental car company doesn’t do payback to the car manufacturer, Unity.

Still not making any sense dude.

You’re overthinking it to win an Internet argument.