True, that meaning seems to be typical now. The opposite is the original meaning though.
> Scores of authors use the phrase “steep learning curve” or “sharp learning curve” in reference to a skill that is difficult to master. . . . Nevertheless, from the standpoint of learning theory, these and other authors have it backward, because a steep learning curve, i.e., a curve with a large positive slope, is associated with a skill that is acquired easily and rapidly (Hopper et al., 2007).
Everyone is talking about curves, but no one's talking about how the axes are labeled.
Based on common usage of the term learning curve, I had thought of it much like a power curve where the y-axis is the amount of cumulative effort you have to put in to reach a particular point on the x-axis, which measures mastery. Sounds like the official definition is effort on the x-axis and the total amount you've learned on the y-axis, which would indeed invert the meaning from how I've understood it.