I think you're still selling archers a bit short:
With items, archers can achieve 17 gymnastics and 16 sniper. [10+2 trained+items] Since they can wear a shield whereas dual wielding characters cannot they don't lose out as much on defense or bonuses as compared to melee characters.
The 17 gymnastics* gives them roughly a 50% chance of achieving 2 or more bonus AP each turn with an 80% chance of earning one bonus AP. 16 Sniper and haste will proc the second attack 86% of the time [compared to the 33% of the time for your dual wielder] so a hasted archer with one +AP item will achieve 3 attacks about 70% of rounds, 2 attacks about 27.4% of rounds, and 1 attack about 2.6% of rounds
Depending on the bow they choose they can either run light on lethal blow and spend the points in tanking/utility or can go heavy into lethal blow to achieve a very high critical strike rate while using a stronger bow.
Quote:
Level 30: 63 skill points
18+2: Bow
10: Gymnastics [+2 trained, +5 items] Total, 17
10: Sniper [+2 trained, +4 items] Total 16: 80% chance of free attack
10: Lethality [+2 items], 12 total
10: Bow Damage
+18 spare points[scrap lethality and use the possessed bow for 28 spare points. Save 10 points on Bow if you decide to buy hardiness.
Bow
Possessed bow 24-62 (5+19d3) Heartstriker bow - attack does critical damage 50%)
or
First Expedition bow 22-66 +2 quick action, +3 bows, +2% HER
Armor:
Sniper's vest 4% +1 dexterity, +2 sniper
Shield:
Quicksilver Bulwark 21% -10% to hit chance, +1 action points, +2 lethal blow
Gloves:
Radiant gauntlets 10% +3% to hit chance
Head:
Cap of farsighted 5% +3% missile damage, +1 sniper
Boots:
Quicksilver sandals 2% +1 action points, +1 strength
Neck:
Nimble chain +1 gymnastics
Cloak:
Deadeye Cloak 4% +1 sniper
Weapon :
Seeking rapier 10-160 + 5% critical hit chance + 5% chance to parry
Ring:
Lightspeed band 6% +2 quick action, +2 gymnastics
Belt:
Girdle of Avoidance 5% +2 dexterity
Pants:
First Expedition greaves8% +8% to evasion, -10% to hit chance, +1 strength, +2 gymnastics
* See the Binomial Distribution P=.1, n=17
http://www.wolframalpha.com/input/?i=binomial+distribution%2817%2C.1%29