From the informatively titled and useful Fifty psychological and psychiatric terms to avoid: a list of inaccurate, misleading, misused, ambiguous, and logically confused words and phrases, it turns out that steep learning curve is one of those phrases that’s the exact opposite of its intended meaning:
Scores of authors use the phrase “steep learning curve” or “sharp learning curve” in reference to a skill that is difficult to master. For example, when referring to the difficulty of learning a complex surgical procedure (endoscopic pituitary surgery), one author team contended that it “requires a steep learning curve.” 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.
Shallow learning curve doesn’t have quite the same ring. But the whole article is actually a goldmine of outdated and inaccurate jargon.