Your 8th GCD GNB opener would never be used optimally due the fact that GNB's have different openers depending on which fight they are in, in 3 of the 4 fights this tier its more optimal to gnashing on the second gcd, because there's a lot more to it than just dummy dps, having to gnashing around mechanics is where the optimisation really lies. Even on Voidwalker, your "extra" blasting zone completely misses raid buff alignment, and if you have trouble with blasting drifting it will easily fall out of your No Mercy.