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The numbers represent contact area, penetration depth, and attack velocity, in that order. For scimitars I'd increase the contact area on both slashing and stabbing attacks, and decrease penetration depth on stabs. That should make scimitars better at removing limbs, but worse at inflicting deep organ damage and penetrating armour.
If I remember my DF combat mechanics correctly, contact area only matters when it is smaller than the size of the thing you are hitting. Limbs aren't that big and the 20000cm^3 size of the blade is pretty large, so increasing contact area won't do anything against human sized non-torso targets. If you want to buff slashing attacks, there are only really two ways of doing it. Increasing velocity (making the attack hit harder), or decreasing the delay between attacks. Increasing velocity is overkill when in the hand of an experienced swordsman (who can lop off limbs easily enough without it), but increasing attack rate is a really big deal. You may have to do some toying around in arena to decide which is more appropriate.
Penetration is in a similar boat. IIRC penetration is simply the depth a cutting attack can go before getting converted to a blunt attack. Anything in excess of the depth required to penetrate through the target is wasted. If you are nerfing penetration, make it a couple of hundred at most and you might get somewhere. In fact, if penetration is measured in centimeters (which is the standard unit for most DF dimensions, but I am not sure in this case), then you probably want to make scimitar stab penetration tiny. See what happens when you do 10 penetration, which is still pretty deep if it is in centimeters.
As for bows, you could try giving them broader heads than crossbows i.e. increase contact area. Crossbows tend to pincusion a target, so having a weapon that is less penetrating but quicker killing against badly armored targets would make them pretty distinct. Again, you will have to test in arena, because I don't know how much upping the contact area to something only a little less tiny will matter.