I also threw easy to both of them teaching them to catch. I used a dart like throwing motion. Neither of them throw like that and both have strong arms.
Every child learns differently and at different rates. There is no magic one size fits all teaching method for anything.
The cookie-cutting you touched upon is right on, maybe you didn't watch the video? I agree with your points- by pointing out an external goal and allowing them to obtain it in their way avoids cookie cutting in the purest form.
The entire process revolves around motor learning and skill acquisition. As soon as your kids pick up a bat or throw a ball, the process begins. Its influenced based on what they see, hear and do.
Emulation plays a role, instruction plays a role,etc...
The cookie cutting comes into play once opinions are introduced. What I view as pleasing would be reflected in others I teach, what you view as pleasing would be influenced in your kids, etc...
Every kid learns differently, moves differently, speaks differently and there is absolutely no "one-way". Anytime you state an external goal, its clear to the athlete. Anytime you exclude "how you do it or perceive it being done" in the form of (cues), it can wreac havoc on the nervous system.
Any form of miscommunication, appears in the form of inefficient movement. Over time, your patterns become ingrained and very stubborn to change. Especially when introduced to higher levels of competition.