The important point is that, if you’re able to readily switch to a different app when your current one changes its payment model, then… do it. Just vote with your wallet, and don’t worry about it. To write a pissy review of an app you liked yesterday, in an attempt to vengefully damage their business, is pretty reprehensible, right? It’s like giving one star on Amazon because the delivery was late. Don’t be a child. Move on.
Ulysses made it very easy, either subscribe or don’t. And if you aren’t interested in paying for a subscription, it doesn’t mean you have to quit using the app entirely. The version you had before the subscription announcement will continue to work until a future operating system update breaks something. And that isn’t likely to happen until iOS 12 is released next year.