> You post screenshots of your app in progress for feedback. Scammer dupes those, rushes app into store, and when you finally launch, they "were there first" and requests your deletion on those grounds.

I seriously doubt this has ever happened in the history of the App Store.

Scammers are "lazy". The look for the easy targets. Copying an existing app is easier and more lucrative than trying to write a new app based just on some in-progress screenshots, as if scammers would even be paying attention to you before you published an app.