Most weapons in ACKS are basically equivalent, doing d6 when used in one hand or d8 in two hands, but this is a deception. There are three tiers of weapons:
Really important weapons
- Spears, polearms, and lances
- Bows and crossbows
- Two-handed d10 weapons, if you have backstab
- d6 one-handed / d8 two-handed stuff that is neither swords nor spears
- Warhammers and axes are slightly special
- d10 / -1 init weapons if you don't have backstab
- Slings and javelins
- Weird combat maneuver-boosting weapons (nets, bolas, whips, flails)
- Staves, clubs, daggers, and darts
Proficiency with swords matters because 21% of magic items are swords, while only 5% of magic items are other weapons. Of miscellaneous magic weapons rolls, 44% are arrows and bolts, 12% axes, 6% daggers, 7% bows, 6% slings, 12% spears, and 13% warhammers. You will find about eleven times as many magic swords as magic spears, warhammers, and axes combined. If you want a magic weapon, you want to be proficient with swords. This is important, because some monsters are straight up immune to nonmagical weapons.
It may seem silly to consider the random loot chart as part of the balance of the game, but I honestly believe that it is. A couple of points of to-hit and damage and the ability to injure otherwise impervious creatures in melee is nothing to sneeze at if applied consistently across most of an adventurer's career. A class that cannot use swords basically gets a penalty to hit and damage in melee compared to those that can, and that penalty grows with level. Magic swords are the original Fighter Damage Bonus. If you reduce the frequency of swords, you reduce the strength of fighter and, more importantly, thief relative to non-sword-using melee classes (namely cleric).
Proficiency with spears and polearms (and I guess lances) is incontestably good. There's a long forum thread complaining about how good spears are, and talking about nerfing cleaving with them. You get reach, you get to first-hit guys closing with you even if they have higher initiative, you can set, you get double damage on charges, you can throw 'em... they're just great, and inexpensive too. The only downside to spears is weight. A melee class without access to spears is seriously impaired while dungeoneering until they get magic swords, and a class that gets spears but not swords is stuck in the second row once people do start getting magic swords. Again, thieves get these and clerics don't.
Bows and crossbows really come into their own in the wilderness levels, when large open spaces with long lines of sight mean you can start reaching out and touching people. Ranged weapons are also an important source of damage against flying monsters. Most of the time the actual maximum range is not as important as the ability to do decent damage to foes about a hundred feet away. A combat class without any real ranged weapons is substantially disadvantaged in the mid-levels, though they probably lose some of their utility once mass combat becomes the norm, because your important targets can start hiding in the mass of bodies. Once more: thieves have these, clerics are stuck with sling, which has -5 to hit at 100 feet and does 30% less damage than a bow.
Two-handed weapons are a weird sort of borderline category. If you have Backstab, they're great and get better with level because your multiplier gets bigger. A 14th-level assassin backstabbing with a two-handed weapon is getting 1d10x5+5 on a hit, which on average one-shots a 7HD monster and has a 10% chance of one-shotting an average 12HD monster or 12HD fighter (and then you can cleave...). Backstabby classes also don't mind the -1 init too much, because they can make up for it with Dex. For fighting classes, the percentage increase in damage is much smaller and diminishes with level as fighter damage bonus increases and the opportunity cost of not using a magic sword and magic shield rises, and the -1 init is harder to put up with because you probably don't have +2 or +3 Dex. They might be good for pushing your average damage up over 9 and 13.5, to be able to reliably cleave 2HD and 3HD foes, I guess? Anyway, two-handed weapons are Situationally Amazing, but generally mediocre for fighters in our experience.
Next, we come to Everything Else. The important ones are axes, hammers, and slings, because they can be magical even if they are less often so than swords. Slings and javelins are both OK as far as they go, but are no substitute for bows or crossbows. The +combat maneuver weapons are mostly weak, because combat maneuvers in ACKS are weak, but I guess if you want a dedicated tripper build whip is what you want.
Finally, we have wizard trash: weapons that deal d4 damage, d6 in two hands, and have crap range (if any).
So what's worth a proficiency?
Each of the Big Three are worth a proficiency, easily and at least. A non-cursed magic sword is at minimum +1 to hit and damage. No proficiency gives you +1 to hit and damage and lets you injure magic-weapons-only foes. No proficiency lets you first-hit closing foes, attack from the second rank, and deal double damage when charging like a spear. And no proficiency lets you hit targets at bow/crossbow ranges with other weapons. These weapons are uniquely good, and you really lose something by giving them up unless you're willing to backfill with Martial Training (in which case, each of the Big Three is worth exactly one proficiency post-chargen).
Two-handed weapons are worth anywhere between +2 and +5 damage if you have Backstab, depending on your level. Looking at thief and assassin, I'm actually inclined to think that two-handed weapons cost a proficiency if you have backstab. Assassin traded away his ability to use shields for them, and thief just doesn't get them. I would not feel bad about making Heavy Weapons Training a thief and nightblade class proficiency. Spears and polearms are also especially good for backstabbers because you can get the extra multiplier from charging. Anything that boosts your maximum damage by 8-10 points is really good.
Once you get down into the OK-tier weapons, I stop caring very much about tradeoffs. Having no access to ranged weapons (javelin, sling) might be worth one. Having no access to potentially-magic OK weapons (sling, axe, warhammer) might be worth one. I dunno.
Meanwhile, trading away armor and shield is tricky, because of how AC's effectiveness scales. Reducing your maximum AC from equipment from 7 to 6 is worth a proficiency. Reducing it from 6 to 4 is worth another. Reducing it from 4 to 2 is worth a third, I guess. Below that, AC hardly matters. I suppose trading it all the way down to 0 might be worth something, because then you can't use magic armor or shields at all, but whatever. It might also be worth considering whether the primary function of a class is melee or ranged, because Explorer and Elven Ranger, for example, with their bonus ranged abilities, were never going to be in the Thin Red Line standing between the orcs and your casters at 1st level.
This gives us the two extremes - thief has three extra proficiencies of weapons (sword, spears, bows) but none of armor (AC2), while cleric has three extra proficiencies of armor (AC7) and none of weapons (none of swords, spears, bows).
Fighting styles: Rolling shield into armor progression complicates these. Two-weapon fighting is pretty marginal (+1 to hit is like... +10% expected damage on average, and only hits +33% if you're at 18+ to hit, in which case you are having a bad day... unless you're two-weapon fighting with magic swords, in which case it could be +5 to hit with Fighting Style), but weapon in both hands is pretty good (d6 -> d8 is like +30% expected damage in the typical non-fighter case, in the absence of other bonuses). I dunno.
I guess at the end of the day I'm not really looking for a coherent build system so much as rough guidelines for "is this reasonably balanced?"
At a first cut, Fighting 2 gets you six points of armor and weapons that you can trade away without incurring an XP penalty: AC7->6, AC6->4, AC4->2, swords, spears, and bows. Assassin traded his AC7->6 for backstabbing with polearms. Bearsarker deserves part of his XP cost increase, with four custom powers in exchange for AC7->6 and loss of bows. Paladins traded away bows and only got one power from fighting tradeoff, so they might be better at 1700 XP (while we're breaking rules, I kind of want to give them d8 HD and raise their XP cost to like 2250 actually). Barbarians traded AC7->6 but all have access to sword, spear, and bow and got four proficiencies, so 2450 XP might be closer. Furies lose swords, spears, and bows and all armor but do keep shields; somewhere in the 2500-2700XP range is probably more reasonable than 3100. Elven rangers and explorers get all weapon groups and trade away some AC, but they're ranged specialists so the AC loss doesn't matter too much. Ruinguards get swords, but not spears or bows, so maybe their XP cost should be 3550 instead of 3850. Does having arcane magic make up for lack of bows? I tend to think no - magic missile a couple of times a day is not really a good substitute for reliable damage with fighter damage bonus (not that they get ranged FDB, either. Trading away ranged damage bonus when you have no decent ranged weapons is precisely the sort of FV tradeoff that should cost XP).
Fighting 1 gets you three points of armor and weapons proficiencies. Two-weapon fighting is not worth much if you don't have swords (all Fighting 1 classes with TWF have swords). Bladedancer works, because they get swords and spears but not bows, equipment AC2, and a proficiency (swashbuckling). Bard is AC2 with all three weapon groups, just like Thief.
So anyways, some things to think about when you're designing custom classes.