Your best moat against low effort copycats? Stamina. Keep your app in the store, update it regularly, add support for new devices, add new features if appropriate, keep marketing and selling it, and keep polishing it. The copycats don't want any part of that. They want to make a quick buck with as little work as possible, hence the copying and plagiarizing. In a matter of weeks or months, unless they're making bank from it, their app will start to rot. If your app has staying power, then you will eventually rise above them all. And when you have another good idea down the road, cross promote between your own apps (but don't be obnoxious about it), and you'll begin to grow a user base who trust you. That's as good a moat against copycats as you could ever get.