Creating a lighter version compatible with previous versions was something that should be considered, since there are many people who have long-standing ipads that use these devices for reading purposes only.
Unfortunately, this is not easy . In order to achieve this, we would have to duplicate several parts of the app, as iOS 9< use API that are incompatible with iOS 12. It’s not easy to support older versions of iOS.
Nevertheless, we’ve checked our Analytics and less than 1% of our users still use iOS 9.
We are supporting the latest 3 mayor iOS versions.