Are you 100% sure? Water ally get 130% from weapon damage (not from my damage) and the active form deal 625% weapon damage per wave.
Also the attack speed of mystic ally should be the same of mine, but for example the waves of water ally seems having a self attack speed (very fast) independently from my a.s. so it seems useless for me to craft any speed on my build.
i.e adding attack speed on my weapon to increase the damage per second is waste on Inna’s water ally build.
Skill damage is based on your damage. And every additive or multiplicative damage modifier. No the waves don’t benefit from IAS (aside from Tasker and Theo, which is a direct IAS for pets) because it’s the pet’s ability, but it benefits from CHC and CHD, ofc +to MA damage, and generic pet damage modifiers like Enforcer gem. IAS is mainly for YOUR other skills like WotHF, CS or DS.
Attack speed serves as a separate damage multiplier for Mystic Ally. Since their attack speed remains the same, they get equivalent damage buff instead.
That’s why build guides suggest Flying Dragon in the cube. It can double the DPS for a short period.