Conclusion - Venom Hydra combined with Blizzard and Magic Missile will do more damage than Arcane Orb.
So you're able to chaincast for 15 seconds before an enemy is going to kill you? I don't think so:)
I don't think a build using AoEs only was designed for maximum stand-still single target DPS either.
However, if you really want to use that scenario, you should include that when using a wand, you can still auto-attack at range as a filler in an Arcane Orb build.
Oh, and you're comparing 3 skills vs 2 skills, doesn't make much sense either, does it?