Interesting discussion, I tried doing an archer slut (i. e. charmer) and went for str agi, presence.
Willpower is good if you have a lot of "spell" ability. I think now every attribute with the spell tag scales with willpower (it used to be more confusing, but I think it got fixed). So unless you take them to damage stuff, you can ignore it. AFAIK debuffs trigger with spellattack, so they may work without high willpower? Maybe? Have to double check.
The highest damage (excluding abilities) would come from the str, agi, cunning spread. Str for raw attack damage, agility for good hit chance and first round, cunning for crits. But you are missing toughness for physical defense, and willpower for tease resist.
IMO your stat spread depends on the role you want your character to take.
Agi/toughness/willpower is a viable support stat spread. You won't be dealing big damage yourself but Brint/Brienne can dish it out for you. You likely get the first turn, and can drop a buff spell.
I have to play around with the bow skills in my next playthrough. They have some interesting support skills, like suppressive fire, or the skill that reduces the cooldown of other skills. I would try to play around with them. Make a save, respec your stats, and fight the lady in front of the winter city. She kicked my butt when stuff did not work out.