In our first year we've found many of the same learnings as this article and have written about our experiences; https://www.magiclasso.co/insights/ad-blocker-year-in-review...
We believe that subscriptions - although currently going through an adjustment and acceptance period - are the future for apps that provide ongoing value.
For apps that don't provide ongoing value, then yes, it may be difficult to survive & one-off payments are probably the only feasible revenue model in those cases.