That's true to an extent, but when discussing the current performance of GPU hardware the context is necessarily software that actually exists rather than hypothetical software that could exist in the future. The high CPU-to-GPU bandwidth is not currently enabling Apple's GPUs to punch above their weight class (GFLOPS or whatever) except in scenarios where competing GPUs simply don't have enough VRAM. In a future where applications are written with Apple's architecture in mind, any advantage this provides would pretty much boil down to using more VRAM because VRAM capacity isn't as limited anymore.