Why do you keep talking about cloud shit? What part of "[they probably don't] require network permission at all" did you not understand?
In fact, if some app's data did "[go] to their cloud," F-Droid would slap a big fat anti-feature warning label on it saying "this app promotes or depends entirely on a non-free network service" and not put an install button in the list in the search results, forcing you to go through an extra step if you still wanted to install it!
I don't know why you're trying to fearmonger so hard when F-Droid really does everything it can to protect you from shit like this, short of actively restricting you itself.