Hello and welcome to the forum 
!
There isn’t much you can do 
. Unfortunately the team took a bad decision: building your app from the greatest supported version instead of the lowest. When you build apps, you usually start with the minimum supported version of the target device, not the other way around.
That said, I think you could:
- Create your own version of cordova that ships with it’s own web view. This may be a lot of work.
- Build your app from the ground up using NativeScript or React Native. It’s not the best option, but certainly better than the first. With this approach you may be able to reuse some (or all) the code (specially with native script).
This options do require more work and you may not have time to do it. I can’t think of other alternatives, but maybe someone else has another alternative .
It may vary from country to country (I’m from Chile), but that’s not only for cheap devices. In my (user) experience, my devices (Samsung mid-tier/high end tier; the same goes to most/all brands?) didn’t receive more than one OS update (from android 4.4 to 5.1, for example, and that’s it; I rooted my devices to install custom ROMs after I knew updates weren’t coming). I’ve moved from Android to iOS just because Apple has a kind of long term support which, at least, continues to update system software.
In regards to ratings, I think if you specify a minimum version (Android 6, for instance), the app should not appear as an option to be installed on Google Play. I know it’s not a solution, but may give you time to rebuild the app.