In New England, on low pitch terrain, at very slow speeds, in an adult group lesson of 1.5 hours, it's very difficult to get a group of grown-ups able to make parallel turns using flex-to-release initiation. There are several ways to get that turn to work, but adult beginners are unfamiliar with all of those movements and they don't happen in the group setting easily. The number of falls increases the group's anxiety. Anxiety leads to rigid bodies, and rigid bodies make for more falls. Some students will get a flexion turn to happen, but it's often a barely-there turn and offers no way for the skier to control its radius easily in that short lesson, thus no user-applied speed control. You can tell I've tried.
Turning in a narrow wedge slows the students down, which makes them happy, and an extend to release or one of its cousins paired with rotation of the skis for turn shape control and speed control is much easier to teach and learn in our New England short lessons.
Instructors who teach out west in day-long lessons will have a different experience.
On the other hand, I've taught 3 and 4 year olds (in private lessons) to make parallel turns on day one in a 1 hour lesson. Actually, they get it in the first 45 minutes, before they wear out.
This is an awesome explanation. Makes perfect sense. It's a matter of what is practically achievable in a naturalistic setting, as opposed to the ideal environment. Thanks