Generated videos used to be hard to edit because the underlying structure wasn't really exposed. You'd nudge something and not know exactly what would shift.
Now every part of the video is a typed element. Click it in the preview and you get the right controls. Edits persist, the preview re-renders only the affected part, and the timeline finally reflects the hierarchy.
Heads-up: videos generated before this release use the old structure. If one looks broken, regenerate it.