Some thoughts from an aero engineer, but admitted helo driver:
The term "on the step" originated with flying boats, I believe. The hull could plow along as a displacement hull with much wave drag, and only make about 15 to 20 knots with max power. As a wave or some forward stick made the hull climb up into a planing mode, (on the forward step of the notched hull) a surge of acceleration is felt as the same power produced much more speed. Today's planing hull pleasure boats illustrate this as well.
In flight, the very draggy flying boats are said to have had almost no cruise speed increase above climb speed when at continuous power (the joke was that the PBY climbed, cruised and descended at 90 mph.) With the aircraft stuck at the bucket (bottom of the drag curve), a gentle dive to the forward edge of the bucket could increase speed by 5 to 10 miles per hour with no measurable power change.
Such conditions will not exist for a modern airliner, with a vast speed range beyond the bucket. In the cruise power range, the power required goes up by the third power of the speed, so even a few knots change will produce a measurable power need (or a descent).