1- Its not calculated using a calc.
2- Its an estimate
3- Its not with woe reduction
4- Its with a quad bloody weapon. Why on earth would you use a double sloted weapon with 170 str.
5- My 9.9k estimate was with the 2 hits, with a 1200% skill damage modification calculated from the atk, with no weapon. Now you come with 16180 with a quad bloody weapon. 9.9k *180% (4hydra) = 17.82k, wich is close with your 16k with hydras.
Idea to make things easier: Looking into the difference, instead on going on skills and gears and etc.
Whats the real difference that we cannot argue about and that will save us time: