Both the abstem and the stem christie were taught as a transition between the wedge christie and the prallel christie. In later years PSIA did away with the abstem and just taught the stem christie. It was one of the ten final forms.
Is the move necessary with todays skis? Not until it is needed.
In the past instructors going for the level-3, besides knowing the theoretical, biomechanical, history and methodological parts of skiing, were presumed to be expert skiers. This may still be true today.
Is anything we needed to know then needed now with modern skis?
Parallel Christie with a preturn or check
Availment in bumps
Expert skiers know how to ski all of these maneuvers and use them subconciously whenever the situation demands.
Forcing carves or even parallel skiing when the slop is too deep and the speed is too slow and while carrying a heavy pack and in unchartered terrain or on unfamiliar steeps says to me that it is time to go back to school.
But you are right, on ballrom manicured blue runs with heavy sidecut skis? Just pick a couple fom the list above