About WebGPU you should look into WebGPU Optimizations | Babylon.js Documentation
It will be a bit slower without any optims due to all the involved caching necessary to handle all the various weirdness possible in WebGL 
@Evgeni_Popov did an amazing job of bringing in a lot of toys to make it faster.
absolute FPS is only the CPU side of the equation and yes renderSorted will be slow as it will sort an array of meshes on every frame which is why it is not done by default.
That said on Mobile are you bound on CPU or GPU if it is CPU, optimizing for might have a counter intuitive result.
What I do not understand is why your GPU time is going up. Are you using more complex shaders or a lot of transparency ? cause overdraw will have a negative impact on some mobile GPUs