This reminded me of a post I read somehwere on the web of a guy who was looking to make some money early on when the App store was a thing and basically poked a

This reminded me of a post I read somehwere on the web of a guy who was looking to make some money early on when the App store was a thing and basically poked around on it trying to do the same thing your list suggests -- find an app that has enough downloads and a decent paid userbase but which seems kinda terrible. Turns out he noticed there was a really popular app for... the bible, but he noticed it was pretty shitty. IIRC, he then made his own without too much effort, published in the app store, and made a decent chunk of change off of it for quite a while.