Bah, damn my mind was jumping around; thinking one thing and I wrote wrong. I definitely admit to this without hesitation and no doubt. LOL!!
Yerazankha, you are exactly right.

(my Dirge's in-combat skills without boon song)
My boon is M1 with zero AA enhancement giving 35 to combat skills; so with boon, it'll be 547p / 570s.

(this is my bud's combat skill out of combat with no boon song in the MT group)
So with Swindler's Luck (+28 p/s/c) and boon song, my bud's in-combat combat skills would be 594p and 610s.
I asked our MT what his in-combat combat skills are in defense stance and no boon song. Bah, I forgot to take a screenshot; best I can recall is that his combat skills were around 470. If ya want a reason for Weapon Boon, then activating Weapon Boon will benefit the tank in defensive stance much more than others since the tank is below the soft cap.
Combat skills soft cap is 6.5 x characterLVL; I have no idea how the 6.5 constant was determined. Soft cap is a relative view point where folk determine the per point benefit is not great. Eventually, there's a point where ya receive extremely little benefit per point; I don't know if 600 would be at this point or not. I think this also could be an accepted justification to not AA enhance Weapon Boon.
At least for me, I thought all of this was interesting so figure I'd share.
Then again, I read that 6.5 x chrLVL is the Hard Cap. Ugh!! I don't know what to think. heh