Unity announced a new fee structure today, and developers are none too happy. “We are introducing a Unity Runtime Fee that is based upon each time a qualifying game is downloaded by an end user,” the company wrote in a blog post announcing the change.
I agree with the essence of your post, but the part about Unity already charging devs proportionally based on sales is not true. The editor is currently licensed per-seats and there is currently no cap to how much money you can make if you run the enterprise license, which is 5k/year per employee.