You are right, I am not a developer of iOS apps, just a consumer. I buy apps where the feature set appeal to me, not promises. I will not jump through hoops like immediately cancelling a sub because the developer doesn't want to offer a one-time purchase.

I use several outdated apps, including Filmic Legacy etc, and am happy - I got what I paid for. Yes, they might stop working at some point. The only thing that bothers me is when the app is intentionally crippled or modified to "encourage" upgrades when it's working perfectly fine.