Speaking of which, I am not sure but does the WS debuff affect the heavily scripted arsenals of the most annoying bosses in the first place?
It only causes their magical, and magical-like abilities to fail. Sequencers, triggers, contingiencies and scripted effects that are applied regardless of what the creature does, are unaffected.
I.E. Beholder rays still work, Ira'Kiou'Dneg time stop contigiency still works, scripted " instant casts when wizards spawn " from SCSII still work.
But all the regular spells fail, even - which makes WS better then others - the truly instant ones, that cant be interrupted by damage, AND all the spells that are scripted to not be canceled by dmg. (and trust me, there are plenty of those in vanilla game, tactics)
I agree tho that ranged WS' damage output is rather low (10-15 dmg per shot) but for parties which already hit like running trains, miscast magic is a blessing.
However remember that on higher lvls, when it is sorcerers, bards and mages who tank enemies, there is a place for more archers.

Take both and compare them yourself
While it is true that BG2 is a caster-heavy game, especially with the nastiest mods, don't forget that many of them are still just run-off-the-mill trash encounters that you will steamroll through. Focus should be on the bosses imo and for those, I'd rather have an Archer and not a WS.
Well now.. My party melts all the dragons (inc ToB) and demogorgon in less then 5 rounds (no HLA's) cause WS prevents them from using stoneskins, pfmg and other defensive spells.
Im about to go through whole game once more, so i'll take an archer with me this time AND a WS, to compare them on field. Even now however i know what results i will get.. Archer deals more damage, while wizard slayer allows the party to unleash hell earlier in 'tough' encounters
Edit :
Protections: I imagine with correctly scripted contingencies, you could become basically unkillable until something runs out. And that is where you can attack, either using the whole array of dispels (AP, Mage, the wand from WK) to create a defense gap or by simply outlasting the buff durations. Getting a shot in before the scripts fire is, imho at least, a bit too weak for my taste - the fun comes from dealing WITH the issue, not circumventing it.
I meant the buffs that mages cast manualy, as mentioned before Contin's and triggers are unaffected.
And last but not least.. Since whole point of having WS is his disrupting attack, which does not get better when levels go up, you can dual him as soon as you can! (be wary of THAC0 tho)
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