NetOne Some interesting findings, I would be curious to see what the results would be like over a wider range of devices.
As for your questions:
1. Are you using Worker mode or DOM mode for your game? Worker mode doesn't work in an Android app, and has some latency for certain interactions that must be performed on the main thread ( audio, mouse and touch to name a few ).
2. It's important to understand that we are actually targeting APK 28 ( Android 9 ) and the value that is set is the minimum supported device version. I'm not exactly sure what optimisations are done for this but my expectations are it affects how your app interacts with dynamically linked libraries. These are software libraries which are already on your device, so they don't have to be included in the APK. Setting a lower version will likely include additional libraries in the APK that are absent on older devices, or may use older API methods that behave differently in terms of performance. There's an outside chance that one APK ends up with more performant memory layout and allocation, but that's something which is going to be very difficult to test and tweak.