Why does it matter what you call it if you can agree on what the movements and the results are? "Bleed over" between skills is not new. Edging movements can change the pressure on skis by introducing G forces. Can ankle movements that don't effect fore/aft weight distribution change ski pressure distribution? Why is there a problem with getting the same result from different movements? One could easily argue that the "waiststeering" movement could also be described as an edge control movement. We do drills all the time where the same movements can be used to develop different skills. We just focus our students on one skill at a time to avoid the confusion. Here we can have the luxury of our discussions being more complete to clarify the confusing points.
There's a whole lot more to talk about when one substitutes the word "can" for the word "does" or the word "does not"
steering can change pressure distribution along an engaged ski edge.
steering does change pressure distribution along an engaged ski edge.
steering does not change pressure distribution along an engaged ski edge.
or what if we said
steering can not change pressure distribution along an engaged ski edge.
Since this is so confusing, is the solution to not talk about it?
Although I agree with Weatherall's definition of steering, I don't think his statement was intended to cover a concept like "waiststeering". My reading of your interpretation of Weatherall's statement is that he is implying that once the edge/pressure requirements are met, all efforts that are trying to twist a ski directly result
in a change of direction of the ski relative to the direction of travel. Until we get to waiststeering, I agree that this is true and it's an important concept. But this is not true for waiststeering. The direct result of a waiststeering movement is a change in pressure distribution. That change is what causes directional change to result. This is similar to over edging creating a tighter turn radius through bending of the ski. Such distinctions may cause confusion, but they are still accurate observations.
We don't need to get hung up over what skill category we pigeon hole these movements into. I'd rather focus on what the movements are, how they work and when to use them.