PoE Mjolner, The Squire, Arcane builds

Path of Building question... as I scrolled past the "Precision" notable on the skill tree I noticed a huge bump in DPS which caught my eye. Was a bit surprised though because I am playing as a manabond hiero with cyclone + arc, so really spell based. I don't recall global accuracy being meaningful to spells. This notable plus the minor before give +10% cast speed as well but was skeptical that addition would result in \~13M+ additional damage. From what I can tell the trigger rate for manabond increases resulting in the higher dps. As a comparable test I added +10% cast speed on a dummy tes