Before adding any Perk or Damage Bonus a DW is capable of doing %14 more damage, per strike(1 strike from each weapon) because 2H weapons can only do %86 more damage than 1H weapon of same class.
I did not count as DPS, it is just per strike, I believe 2H has much lower value in terms of DPS.
Looking at Perks, there are only two difference:
1-) 2H has 9 items, 1H has 10 items, that 1 extra item is Dual Flurry which gives %35 more speed.
2-) 70 kill perk of 1H gives %50 more damage with Power Attacks, 70 kill perk of 2H only gives directional swing.
Looking at Enchantments:
Enchantments in game are powerful, and 1H & 2H enchantments are not different, so DW has 2x as much enchantment power as 2H.
Plus thanks to their faster speed, they can apply enchantment effects much, much faster.
Looking at Shouts:
Elemental Fury which increases speed, at first glance it should help 2H more since it is % based, but if we add the fact DW getting 2x enchantment, their apply rates getting boost from that too, which makes DW literally invincible.
Looking at other abilities:
Yes, 1 Handed cannot use Block/Bash, but have you ever thought, you're capable of getting bonus from Stealth while 2 Handed cannot that's why I believe Dual Wield is overpowered.
2H has Block/Bash, Dual Wield has Sneaking Bonus.
2H has longer reach, Dual Wield has quicker animations so they can evade enemy attacks more easily.
EDIT: Changed whole article to further support my argument logically.