Given what one can do when trusting a walled garden, and can't without, is there some reasonable concern critics overlook? Say, apps having access to other app

Given what one can do when trusting a walled garden, and can't without, is there some reasonable concern critics overlook? Say, apps having access to other apps' data could unfairly modify cached user data, frustrating legitimate multiplayer gameplay? i.e.: write an app which auto-maximizes all player capability stats? To wit: cheats may become easy to perpetrate and hard to block when full sandbox access is not prevented.