AFAIK there have been very significant changes since I left IMG, so it's likely different and doesn't have a single huge bottleneck anymore, but in an early version, I tried disabling the foliage (many alpha tested layers with an ALU-heavy pixel shader) by modifying the vertex shader to output a dummy position. The overall performance of the entire benchmark increased by about 3x on all handheld architectures.
Also somewhat annoying that the Exynos Galaxy S4 (and maybe other Android SGX devices?) fails to compile all the GLB2.7 shaders so it's impossible to benchmark. James, this is a disgrace, how dare you prioritise compiler optimisation over bugfixing! Oh wait, oops
So is Alpha blending a weakness of the Series 5 PowerVR GPUs, compared to the Adreno 320, and would it account for the drop in relative performance in 2.7 vs 2.5.1 for Power VR equipped devices?