I've no doubt any student paying attention will recognize the greater drag in a Wedge vs. a Parallel turn - but if all we're teaching is a Wedge turn they'll have nothing to compare it with! Further, I like to direct their attention to the feathering of that outside-ski as their 'speed control' mechanism rather than the Wedge's opposing edges. This causes them to focus on controlling that ski's position and controlling its ski/drift rather than creating a focus on making the Wedge bigger when they need speed control.
I don't think the drag of a Wedge is even mentioned in current PSIA materials as a relevant component. In the Alpine Manual (pg. 65-66) there is no mention of drag or speed control attributes in a Wedge. In fact, the last point (#7) ends with, "... Control turn speed with turn shape, rather than the size of the Wedge."
I'm not saying that drag doesn't exist nor that students wont use it once they find it - just that we should minimize Wedge drag by encouraging flatter skis and an minimal Wedge angle, forcing (enabling!!) students to use other, more favorable techniques for direction and speed control.
With that in mind, re-read your second paragraph from the perspective of taking beginners out on a *truly Green* run (nearly flat). If on a true Green run then I think students will not experience enough acceleration for 'drag' (sped control via friction) to be an issue and they'll be able to focus on directional control rather than speed control.
Of course, if all we have available is Blueish-Green terrain, then we're probably stuck with students grabbing onto friction anywhere they find it. If so, I think we need to make a special effort to point them toward skidding that outside-ski as the preferred source of fiction.