The reduced proc coefficient is just a drop in the bucket, and overall wizards are seeing their fair share of buffing.
In addition to the Hydra buffs, we're also increasing the damage of some lesser used Signature skill runes. A few skills are very popular right now such as Seeker (Magic Missile) and Piercing Orb (Shock Pulse), so we’ll be buffing the other runes to match. We'll be revisiting all of the other Signature skill runes with much the same philosophy as Hydra.
Meteor and Arcane Torrent are both going to get buffs, as well, since neither of those feel strong enough to justify the Arcane Power expenditure.
Base damage increased from 200% + 60% over 3 seconds to 260% + 60% over 3 seconds
Molten Impact damage increased from 260% +78% over 3 seconds to 390% + 90% over 3 seconds
Meteor Shower damage increased from 80% to 104% for each smaller Meteor
Comet damage (of initial hit) increased from 240% to 312%
Arcane Power cost reduced from 20 to 16
Base damage increased from 175% to 210%
Arcane Mines damage increased from 150% to 180%
Cascade damage increased from 175% to 210%
Death Blossom projectiles are now less random
Meteor requires the player to correctly predict enemy movement in order to deal maximum damage, and Arcane Torrent requires you to stand still for extended periods of time to do damage. Since a player is putting in some extra effort to use these skills, some extra damage seems justified.