Could you also compare dual wield wand vs bow and crossbow, please?
It's actually not
quite as bad as the figures above, but it's still comparably weak. At 55 INT, 15 in Pyro and two lvl 21 fire wands, (wands scale with the school of the same element) the main hand was hitting for 550 average and the off hand 300 non crit. Wands crit without the Savage Sortilege talent too. With more optimized gear, you could probably get better results, but the difference won't be huge. There's also not really any reason to compare bows to crossbows. Crossbows always do more damage and have a closer damage range (meaning their min - max damage is much less spread out like how the bow is). You get a -1 movement penalty, but it doesn't matter at all.
Sheet damage is only 1106 - 1344 too. It's 70% - 80% higher on the Ranger and Rogue. This is without investing any into the actual Dual Wield Mastery, but I have no idea why you would even do that with a Mage since it's going to raise your damage less on average than the other alternatives.