In the traditional, original sense of the term, learning curves are (presumably) asymptotic to a horizontal line representing total competence.

Somehow, sloppily, "steep" has come to mean difficult to learn, rather than quick to learn.

In the original version: A steep learning curve means quick learning at the beginning. A shallow curve means that it takes a long time to build up skill.

You're just rephrasing nonsense. What is "the efficiency gain is exponential" supposed to mean, in concrete terms? This is just empty manager-speak.

/s