AbdulAlhazred
Legend
Just quoted the above build here.
Hrmmm...let me see. A 12th level Barbarian has 3 ASIs. If one feat (GWM) that becomes 2, if two feats (Sentinel), that becomes 1.
Human Totem Barbarian with Standard Array is:
15, 14, 16, 9, 13, 11. Assume you go 3 ASIs instead of feats. You put the 16 in Con. You put the 15 in Str and the 14 in Dex. ASI you go Con > Con > split Str/and the 13 (probably Wis).
Your Unarmored Defense AC is then 10 + 5 + 2 = 17. I guess if you aren't going GWF then you're going to want a shield. Shield +1 gets you to that AC 20.
You're HPs are another +2/level for 144ish with halved damage.
Weapon +2 nets you +4 (Prof) +3 (Str) + 2 (Ench) = +9 hit @ d8 +3 (Str) +3 (Rage) +2 (Enc) = 13.5 ave damage @ 80 % hit rate * 2 attacks.
This guy is beefy no doubt. However...
He can't go Reckless Attack against this number of enemies (return is terrible and the cost is significant). His offense is not great. There is a fairly strong chance this guy is only killing one enemy per round.
He isn't sticky at all. He literally has no melee control. At 14th level, prone as Bonus Action comes online. Good stuff. But 0 control without feats.
The main deal here though is the Wolf Totem Warrior effect. That would give the GWF Advantage on most attacks. That plus Bless will turn the Fighter into a terror.
I assumed he would be built as a 2H weapon berserker with control, but we can go with this I suppose.
Now the Human Champion Fighter, assume something like:
16, 13, 15, 11, 9, 14. GWF + HAM + PAM + 2 ASI; +2 Str > +1 Str/Con. +1 Plate for 19 AC. +2 Halberd/Glaive.
With Tunnel Stalker, GWF, PAM, +5 Str, +2 polearm, Advantage on most attacks (Wolf Totem Barb) and Bless, this guy is your melee control and meat-grinder. Also -3 damage per/attack due to HAM.
I'm still seeing 30 % and 35 % hit rates against these guys. And again, if the Barbarian goes to a build that is more effective in this scenario (IMO and especially so with the cleric in play here), he is going to be hit on a 10 - 12 (12 if the rare magic item becomes Bracers of Defense rather than +2 weapon).
Also, if they aren't keeping up with the waves (which seems very possible at some point with the above builds), the prospects for Help Actions (or Help + Grapple) by the Orcs goes up which could possibly turn into problem (that the cleric would have to bail them out of, assuming it isn't in trouble itself as the "reapers" get behind).
I think a fair bit of it depends on the control here. I don't like this Barbarian build above (no control and paltry offense...basically blocking terrain, a buff-bot, and maybe averaging taking out 1 of the 4 orcs). You put two warriors who can (a) be blocking terrain, (b) make the melee sticky and punish foes who violate their control, and (c) have the offensive output to keep up with the waves without being overrun, it becomes doable.
If a - c fall apart, the orcs overrun the town, or waylay (and possibly kill) the cleric (even though a War Cleric is so stout), become too many in number rendering the DPR input too significant to keep up with...or a combination of the above.
But I think with the right builds (sub defensive Barb for offensive one without Reckless Attack), a - c can be maintained and the Cleric can sustain the two reaping juggernauts for a long, long time.
If I can find some time, I'm going to impose my will on one of my players to run this with a War or Life Cleric.
I still see the hit rate being higher than the 25 %. I think 30/35 or better (assuming an offensive Barbarian) is more realistic.
Also, consider the default sticky melee in AD&D.
Also, while the 1 attack/character level wouldn't apply to orcs, they would apply to most all canon fodder in AD&D.
Finally, consider the AD&D 2e Fighter. The Heroic Fray rules extend that to Level - 10 in HD so it would apply to orcs for level 12 Fighters. And the AD&D 2e weapon spec train had one destination; pain. I feel pretty confident that both the AD&D 1e and the AD&D 2e Fighter would soundly defeat the 5e analogue in this scenario.
I've never even HEARD of 'Heroic Fray' and I ran 10 years of 2e, so that tells you something of my general contempt for 2e supplements (almost universal garbage and not IMHO to be considered as a normal part of the game, though if you invoke some of the 'Complete' series stuff I'm not quite so opposed, most of that is under-powered though). Weapon specialization will help the 2e fighters insomuch as they gain in attacks per round, and they could also dual wield, etc. AD&D fighters are also VERY magic item dependent. The results could vary drastically depending on item loadout.
As a somewhat extreme example my 14th level Ranger (built in 1e, but I think 2e was in force by then) had vampiric regeneration and some other stupid tricks. He would literally GAIN hit points in this scenario and could fight forever, or until the GM ruled otherwise. In fact if you replaced the orcs with ogres he'd actually GAIN from the exchange (more hit points to reap faster and higher damage output). Make them Demogorgon worshippers, his sworn enemy, and you'd have to count the ogre deaths on 2 hands every round. Pairing him with a cleric and another melee combatant would be redundant. We actually played out basically this scenario, it wasn't pretty. I think we finally decided the bad guys gave up after I hit about 5000 hit points.