Rather than using benchmarks for the GPU, look at existing cross-platform applications with similar performance and see how it compares. Install it on your computer to make sure the intensiveness is similar (using whatever benchmarks you want), then install it on your android device to see if it can keep up to your expectations. You can find benchmarking apps or you can use the profilers on Android Studio to see how the device in question is handling the application.
This is about as good as you’re going to get. Like you said, so much relies on the implementation and the vastly different architecture. Lastly, if you’re building on a framework that builds to other platforms (libgdx, xamarin, etc), you should present a specific question to other users of that framework.
solved How to predict performance of a program for smartphones developed on a pc