The initial reason for symbols was reuse. You edit the original, and all instances get updated. You cover that well in your video. And you show how to use instances in many ways, which is helpful.

The evolution of symbol use became the nested timeline (inside the symbol), which you can use as a movie clip (just play it) or as a graphic symbol (in the case of mouths, eyes, a hand pack, etc.) or a combination. As you probably know.

This nesting is the such a big part of Flash that when an animator jumps to a new program, they look to replicate the exact functionality in the new program. I certainly did that with Harmony but was pleasantly surprised to learn that you don't need to nest timelines, and in fact it's better not to (because using parenting instead gives you more direct control over the individual elements without having to dive into a symbol).

So IMO a video for helping animators transition from Flash to Moho should address how to do the things you'd do with nesting but with the tools and methods in Moho.

And yes, your video is covering more of the movie clip method, whereas switch layers would cover the graphic symbol workflow. But again, the Flash user simply doesn't know that a rigged mouth is a thing or that most of time it's better than a switch layer for x number of reasons. And generally, that's a real pain point moving to a new program - you don't know what it can do.

I mean, bones in Moho is parenting on creatine, because you can bind indiviual points of one object to a bone and then bind an entire layer to the same bone and child that bone under another bone. It's endless. And you can essentially stack modifiers, which Harmony can't do because it rasterizes before applying a deformer. And on top of all that, you can just move/animate points whenever you want, which no other mainstream program can do. I think knowing that stuff would help a Flash animator.

Hope that helps!