On desktops, a good app is often more than $20-30 with a new major release each year that is not free. The cost is very similar to subscription costs. But, even that is might not enough on iOS. As I said, these devs are not greedy, they want to make a sustainable business. In turn, they offer support and continued development - which is good.
“Debatable”
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Why debatable? It is used by many professional comic, manga and concept artists around the world to earn money. If there is a good example of a professional app - this is it. And the iPad version is fully featured.
They could, but most people probably wouldn’t pay for it. Or would expect lifetime updates and freak out when asked for more money for the next version. I remember the drama when Things, a $10 todo app, didn’t give a new major release for free after two years. It was really sad. People just don’t want to pay up front for quality apps on iOS. I don’t know why that is, but subscription models seem to be the solution. Otherwise, you’d have low quality apps. In case of illustration apps, just compare iPad apps and Android tablet apps - to get a clear picture what the situation would be like.
Fight how? You do understand this model works and is not going anywhere soon? In fact, it will only become more and more present, as everything is slowly becoming a service - which is sometimes good, sometimes bad. Bud good or bad, it’s how things are.
You can accept it, or not use great apps.
And seriously, $25 a year for an app like Clip Studio Paint is a bargain, no matter your personal feelings about the monetization model.