It's not, as far as I know, but only five tiers difference, that's borderline worth using dw instead of 2h, with 2h the higher-tiered.
Concentrated Blast is a 5s cooldown ability with 200% weapon damage over 4 ticks, or 300% over 6 ticks (I think). That's equivalent to 150% damage, better than Wrack, Sonic Blast, Impact (on stunnable targets) and Chain (if there is one target only). Dragon Breath, Asphyxiate, Wild Magic and Sunshine are all better, not sure about Combust, it's probably around the same.
If you assume that a t85 weapon is some 1900 damage (average of t80 and t90), it's a 6% boost over a t80 weapon.
Since Concentrated Blast is such a big boost, dw beats 2h at nearby tiers, but I don't know how the lower adrenaline gain (8% per 4 or 6 ticks) works out when using Sunshine/Metamorphosis and such.
Supporter of Zaros | Quest Cape owner since 22 may 2010 | No skills below 99 | Total level 2595 | Completionist Cape owner since 17th June 2013 | Suggestions
99 summoning (18th June 2011, previously untrimmed) | 99 farming (14th July 2011) | 99 prayer (8th September 2011) | 99 constitution (10th September 2011) | 99 dungeoneering (15th November 2011)
99 ranged (28th November 2011) | 99 attack, 99 defence, 99 strength (11th December 2011) | 99 slayer (18th December 2011) | 99 magic (22nd December 2011) | 99 construction (16th March 2012)
99 herblore (22nd March 2012) | 99 firemaking (26th March 2012) | 99 cooking (2nd July 2012) | 99 runecrafting (12th March 2012) | 99 crafting (26th August 2012) | 99 agility (19th November 2012)
99 woodcutting (22nd November 2012) | 99 fletching (31st December 2012) | 99 thieving (3rd January 2013) | 99 hunter (11th January 2013) | 99 mining (21st January 2013) | 99 fishing (21st January 2013)
99 smithing (21st January 2013) | 120 dungeoneering (17th June 2013) | 99 divination (24th November 2013)
Tormented demon drops: twenty effigies, nine pairs of claws, two dragon armour slices and one elite clue | Dagannoth king drops: two dragon hatchets, two elite clues, one archer ring and one warrior ring
Glacor drops: four pairs of ragefire boots, one pair of steadfast boots, six effigies, two hundred lots of Armadyl shards, three elite clues | Nex split: Torva boots | Kalphite King split: off-hand drygore mace
30/30 Shattered Heart statues completed | 16/16 Court Cases completed | 25/25 Choc Chimp Ices delivered | 500/500 Vyrewatch burned | 584/584 tasks completed | 4000/4000 chompies hunted