Imagine an education system in which numerical and letter grades was nonexistent; Good or bad idea?

As you said, it has a lot to do with efficiency. Colleges move people through like cattle, in a sense. They often have large cles and need a quick and effective way to tell people whether or not they suck. And they need to base your progress on something tangible in order to deem you worthy for a diploma, thus worthy of a position in the field of your "expertise". A private college might be able to pull-off your idea, which isn't a bad one, it seems like a clic approach. However, as important as I feel it might be for me or the President of the United States, I don't agree that everyone should be forced to deal with the mes. There are plenty of jobs for introverts.