Isn't your "Damage" just your basic weapon damage averaged out, taking in to account things like attack speed and crit rate? So if you have 10k Damage and use Arcane Hydra for an hour, it'll do an average of 10k * 245% = 24.5k DPS with most attacks being lower than that, and crits substantially higher?
Then if you have a 10% boost to Arcane and/or Hydras, you'd then apply those to the 24.5K DPS to see what kind of damage you can do with your hydra. This is the additional math people want done for them? Seems like the biggest obstacle is finding somewhere to display it. What if instead of "245% weapon damage," the description for Arcane Hydra read, "245% (296%) weapon damage," assuming you have +10% Arcane and +10% Hydra slotted? That'd give you a direct comparison to other skill choices at least, like if you're trying to choose between hydras and torrents for that last slot.
Howzzat sound?