I’ve certainly vanquished orc camps containing 20-30 orcs, including a warlord and lots of warriors, with little in the way of injuries/casualties and without using any very fancy or specific build – mostly an even mix of shieldlings and bow/billhook/longaxe-wielders, with the odd reach-advantaged 2-hander chucked in. For battles against orcs, I always keep everyone in a tight formation that can’t be readily knocked out of place (usually 5 in front and 7 behind) and always leave everyone in place (at least early in the battle) until an orc closes in (to stun or not).
I never use a sergeant/rallier (not because it isn’t expedient, but because it seems unrealistic). Instead I try to give everyone an individually high/adequate resolve.
My ranks aren’t by any means comprised exclusively of guys with 2/3-star talent for their primary attack and defence skills. Some of the shield-bearing front-liners (often Wildmen or Prizefighters) start with mediocre melee attack/defence skills and no talents, but they have lots of hit points, lots of resolve, lots of max fatigue, lots of armour, heavy metal shields for battle against orcs (kites for goblins and heaters for bandits and most others), and have the perks to increase the durability of their shields and armour. Their main function is to get in the way (and to amplify the hit-chances of back-stabbing back-liners with higher skills/talents and more devastating weapons). However, once they’re at/approaching level 11, their melee attack and defence are often pretty impressive anyway, and I can give them Backstabber and/or Fast Adaptation for their final perk(s) if they could still do with a boost. You don’t generally need astronomic melee skill to hit orcs anyway. Also, I never use shieldwall against orcs, and only level-up melee defence when it’s a +3, but the combination of durable shield + moderate base defence + high hit points and resolve + heavy armour and Battle Forged means that they can easily take a few hits (but they rarely need to take as many as they’re able to take). I give everyone in the company the Hold Out perk, even if they do have excellent all-round defence skills, since I don’t want a lucky hit to impair their abilities.
Some of the front-liners use only swords or spears, which would be highly laborious against heavy orc armour on their own, but actually work well enough in combination with the billhooks and/or longaxes of the back-liners (plus the hammers/maces/axes or occasional great-swords/axes/hammers used by the front-liners with especially high melee skill). The back-liners are quick-handers who wound the orc young/berserkers with ranged weapons before switching to 2-tile weapons. It doesn’t take long for swords/spears to put the lightly-armoured orcs on the brink of death, and then the backliners can finish them off, go Berserk, and use their extra action points to break through the armour of the warriors. Once the warriors are running short on armour, swords et al can eat away at their hit points.
Once the warriors get frustrated and push their way through the ranks to my back-liners, the back-liners (including the dead-aim archers with rare ranged skill) stand their ground and fight (typically in medium armour) with billhooks or longaxes. It can be risky, but it makes battles more tense and exciting. At that point, the warriors are super-easy to hit thanks to Backstabber + Surrounded, and all of my guys with 2-tile weapons can concentrate their attacks on whichever orc is currently posing the biggest threat to life and limb. The occasional casualty creates a vacancy for an exciting new prospect.
Almost all of the back-liners have the Berserk perk, but they don’t require exceptionally high max fatigue, since an extra strike costs only 15 fatigue, and you aren’t going to slay a heavily-armoured orc on every turn anyway. Since I don’t keep them away from the melee when it comes, I usually level-up their melee defence when it’s a +3. I always level-up their ranged skill and melee skill when they are +3 or higher, and, at the start, I always level-up their ranged defence when it’s +3, but I might stop once it’s adequately high and they already have the Anticipation + Dodge perks in addition to decent armour. Typically, I focus on making the back-liners elusive and hard-to-hit at the start of their careers (e.g. Pathfinder, Dodge, Anticipation), and then on making them more proficient at hitting/damaging things (e.g. weapon mastery, Bullseye, Backstabber), and then on making them a more explosive dual threat (e.g. Quick Hands, Backstabber), and finally on improving weaknesses and/or amplifying strengths. I usually give Bullseye only to the more specialist archers with the highest ranged skill; the others use crossbows when there’s a good line of sight, wear heavier armour, and tend to be more focussed on melee attack (e.g. I might give them Fast Adaptation, Quick Hands and Backstabber for their first 3 perks). I don’t usually give back-liners mastery of a melee weapon, but I might give Axe Mastery to ones with high melee skill and max fatigue, and let them carry spare great-axes for extra excitement in orcish encounters. Wildmen and prizefighters make great back-liners if they have appropriate talents, but most of my back-liners tend to be hunters (plus sell-swords as the game progresses).
I also usually have a few elusive, light-armed, high-initiative guys (e.g. thieves, gamblers) whose primary function is to be annoying bastards (e.g. chasing archers/ambushers, enticing 2-handers into clear lines of sight, cornering necromancers). Since these guys tend to be away from the main fight, you can give them the Lone Wolf perk to increase their defence skills further. A similar role could be played, by otherwise untalented/expendable characters with decent max fatigue, making use of nets and the Adrenaline perk (and Footwork if they ever get that far). Obviously, these characters are of limited use against orcs, and are more useful in the early game when most people have light armour and low defence skills.
I haven’t ever managed to incorporate many 1-tile 2-handers into my companies, but I usually have the odd one or two (typically a sell-sword or hedge knight, but it could be anyone with 2/3-star melee skill). I’ve found that they don’t necessarily need to have high melee defence, and don’t necessarily need to use Reach Advantage, and that great-hammers are awe-inspiring instruments of maim-ment. If you have someone with super-high melee skill and max fatigue but crap defence skills (e.g. a talented wildman), you can give them a tonne of armour (+ Battle Forged) so that they can’t get poisoned by goblins and will almost always devastate their foes before being devastated themselves. Eventually you could also give them Indomitable, so that orcs can’t stun or isolate them, and to diminish damage on rare occasions when they become vulnerable (the same could go for a Duelist character). If you have someone with excellent melee skill and good defence skills/talents but poor max fatigue (i.e. most swordmasters), you can give them plenty of armour and good ranged defence (+ Anticipation), forego Berserk and Reach Advantage, and just let them patiently smite their enemies with a great-hammer once per round, never accumulating too much fatigue. Great-hammers do less raw damage to hit points than -axes and -swords, and cannot so readily/extensively be used for AoE attacks, but they leave anyone hit in an almost utterly ineffective state (but still alive and in the way of fresher and more effective comrades).
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