Edit: Updated to fix a couple of math errors and boneheaded calculations. Still no promises this is right, it isn't agreeing with fsim.
Yeah, I've been looking over the launcher damage formula quite a bit while playing my last hunter. Some parts just don't make sense though, like A: A is min(3, skill/3). So A maxes out at 9 skill, and can never go above 3? It then adds 3/16 to your average damage, but also 3/2 afterwards (Why isn't that just one term?).
Going to work through the formula for my 45 strength +9 damage crossbow:
The first part of the formula is where it picks the lower of (str - 10)*(2B+A)*C vs (L+1)/4. For crossbows/longbows, B is 9.5, A we'll assume is 3 because your skill is > 9, so with enough strength, the first part, (str-10)*(2B+A) will usually be higher for slings/bows. Crossbows first term is always 0, so they never get to use L+1/4. For Slings/bows with a +9 weapon, add is 2.5 damage. Then add 4.75(fixed) + 1/8 enchantment(1.125 here) + 3/16(for anyone with >9 skill) and you get 6.0625. Now's probably a good time to mention I have no idea how crawl does rounding, I'll assume it isn't rounding intermediate values and only rounds to an integer at the end.
This 6.0625 then gets multiplied by (1+skill)/44, so with 21 skill it's cut in half to ~3, or with 27 skill it comes out to 3.85 average damage. I was using an elec crossbow, so that's final, but let's assume I had stuck with the velocity crossbow for 20% bonus damage: 4.62 damage at skill 27. Add slaying/4, for most of the end game I had around +5, so 5.87, and 1.5 for any skill > 9, and you're at 7.37, and then for crossbow only, add half the enchantment again, so 11.87 with the +9.
Used a troll since my local doesn't have formicids, but in any case: with 45 str (and 30 dex/int if that matters) and using fsim against a yak:
+0/+0 crossbow of velocity
level 5 skill: 5.7 average damage, 21 max
level 9 skill: 6.9, 24
level 13: 7.7, 27
level 27: 9.5, 39
+9/+9 crossbow of velocity
level 5 skill: 11.7 average, 38 max.
level 9: 13.2, 42
level13: 13.8, 42
level 27: 16.2, 48
So it seems like my calculation is quite a bit off, 11.8 vs 16.2, but both ways demonstrate how small of an impact skill has on damage. There really isn't that much incentive to train a ranged weapon past level 9 if you are able to reach min delay. With high stats, you can, anyone with lower stats, once you reach min delay, just stop.
This works out to about half the average damage from a 2h weapon like bardiche, although apparently the max damage on the bardiche is about 4 times higher.
- but for bows and slings you need a certain amount of str to take full advantage of enchantment
Edit: I missed the C in the formula, this is right
Interestingly, you don't need any strength to get the full effect from crossbow enchantment, and crossbows get roughly double the effect (see below).
each point of damage enchantment is +buttload average damage
Actually it seems like each enchantment is +.375 damage, which is pretty close to the .25 slaying bonus. The exception to this is crossbows only, where enchantment is .625. I'm not sure I'd call that a buttload, but it is a bit more than double what slaying gives.