I'd like to do a different experiment with world builder. What would be good variables?
-Equal Hammers of Mace & Trebs vs. Chuks
-A city with 60%? Defense (No hill?)
-Half as many hammers worth of Longbows (maybe more?)
-Drill 3 Chuks, Combat 1 CR2 Maces & Barrage + Accuracy Trebs
List any more if needed
Taking a lightly defended city isn't a big deal - one stack is as good as another for easy targets.
I'd make it a city with 60% cultural defense, walled, on a hill, that can produce another longbow every 2-3 turns.
The real advantage of cho-ku-nus is that you get them before Maces and Trebuchets.
A "more realistic" test would have the maces and trebs facing a slightly more advanced and better garrisoned city.
A decent sized stack for the era would have around 10 attackers minimum, with 4 accuracy promoted catapaults. Ideally they are not attacking at all - they're there to remove city defenses. Trebuchets get city raider promotions, not barrage.
The point of the test (I assume) is to take a highly defended, strategically important city and be able to continue the campaign. It's not to simply take out one city.
You're likely to face 5 or 6 longbows and maybe a few axes/swords or regular archers. If they have catapaults of their own, the drill-promoted Cho-ku-nus are at at further advantage since they are resistant to collateral damage.
Entering borders at a 60% defense city means crossing at least two tiles, maybe 3. That means expect at least one more whipped unit and maybe reinforcements coming via the roads. So make it 6-7 longbows, with another coming in 2 turns if the city isn't taken.
I don't think the test would have to be done 20 times - 3 or 4 times would be enough to give a good indication of which stack preserves more hammers.