When it comes to archer, GET ROGUE <---, only Dex gives Att rating for archery, making it the primary stats.
Reason u shouldnt use warrior is as follows:
#1 Str does nothing for att rating, hence high str is useless, the only benefit for having high str is to use high lvl armor. how ever massive armor has a sick reduction on attack speed and u should not consider using it.
#2 the ONLY specialization warrior has that benefit archer is champion spec's Rally. and since u are often on the far back its radius doesnt help any of ur other melee's, making it a poor spec to have. while compare to rogues u have access to Dueling from the duelist spec, if specced deeper it is very similar to the benefit of champion's rally. and u have access to Bard, Song of courage significantly increase archery dmg and crit for the whole party, very beneficial. Ranger spec is also a good choice, the summon is quite strong and does reasonable amount of dmg. the combined dmg is very promising.
#3, As warrior u cant use red Jenny's striker, a glove with 15% crit dmg/back stab dmg glove, there is no gloves which warrior has access to that increase ur dmg like that one. the most powerful archer boots cadash stomper is also a leather boot, making it less attractive for warrior.
#4, As archer your best DPS skill is Arrow of Slaying + Scatter shot, scattershot has sick threat value, making u the target for every one in the room. best countered by "stealth". as warrior u have to tank it, disengage's range is sad.
Things to know as archer:
#1, you need loads of att rating to be effective, 130-140 around lvl 20 is what u need to aim for with buffs. (champion's Rally with motivate from your Melee warrior helps)
#2, scattershot has crazy aoe dmg, use often.
#3, This is the most important of them all, NOTHING STACKS WITH RAPID AIM <--, this means if u have a bow or item with rapid aim, u dont need to activate ur rapid aim ability, because it doesnt stack. and this automaticly make items with rapid aim very useful to have, because it allows u to fire the same rate as with rapid aim(talent) enabled. but with Crits <--. and ofcourse stuff like haste is not useful at all for archer.
Best Items for Archer:
#1 Best Longbow in game is called Far song, can only be obtained if u have killed owen during the redcliff quest, Use this + The Long Sight (5% ranged crit helmet)
#2 Best Shortbow in game is called The Dark Moon, obtained in Dalish elf shop. if u use this u have to combine it with Armsman's Tensioner (same shop after gathering all the allies).
#3 Best Crossbow is the Antivan Warden crossbow in the warden keep DLC.
#4 eventhough the only armor that gives Crit dmg % is the warden commanders plate, it is alot better to just use felon's coat, due to the att speed penalty from massive armors.