Hey look! Is that a grenade?
In all of skiing, no other words are more misunderstood than the concept of under/over edged.
If it is described as having excessive leverage or a lack of leverage, it begins to make more sense.
The most commonly recognized method of determining the need for canting involves referencing center of knee mass relative to mid line of foot.
The person who is described as underedged will typically stand in their boots with the CKM inside the midline of their feet. This causes internal rotation of the leg (and ski) and decreases their leverage on the ski.
The skis turn easily, but they don't edge.
The person who is described as overedged will typically stand in their boots with the CKM outside the midline of their feet. This causes external rotation of the leg and increases leverage on the ski.
People who are underegded have more trouble in the bottom half of the turn, people who are overedged,have more trouble in the initiation phase.
There is a significant rotational component that is equally involved in the equation as well. It's not just a lateral thing.
A simple on snow indicator can be a shallow angled one footed traverse. This works best on a >15 meter ski.
The underlevered skier will tend to have the ski twist underneath them and skid across the hill.
The overlevered skier will have the ski engage and try to turn up the hill.
The experienced skier will create compensatory movements to allow the ski to do the task. The skilled observer will see that.
The person who is standing reasonably well will do the task quite simply almost regardless of skill level.
Does that mean you need canting? No of course not. It might indicate you are not standing as well as you could be. But it doesn't tell you what or where the problem might be.
There are stereotypes about bowlegged people being overedged and knock kneed , pronated people being underedged, but it turns out people come in a tremendous variety of configurations.
From there it get's complicated, but that keeps it interesting.