Probably the right answer is some combination of

- editorial (although this can be gamed in a different way - a bunch of PR/marketing folks with strong relationships with Apple employees would suffice),

- reviews/ratings (also gameable)

- some algo for how long users continue to own/open/use an app after they download it (almost impossible to game, because it's linked to fundamental use).

With this combo - the rich will still get richer, but at least they will continue to be quality.