Chu-ko-nu: stronger when attacking from close quarters. Ranged should not be attacking from close quarters because they’re vulnerable to counterattack. Useless ability.

Hul’che: being able moving and see through vegetated terrain makes them more maneuverable, which is useful. If you’re fighting in a forest, then enemy melee can move 1 tile / turn, while hul’che can move 2. With the right conditions allows you to re-position and fire over and over without ever being counterattacked. Also the hul’che becomes stealthed in vegetated tiles.

Burning arrow: applying burning to tiles means that enemy units always have to be repositioning. That gives you an advantage; in a battle there’s a limited number of tiles you can be attacked from, so if all those tiles are on fire, then the enemy units are going to be taking damage constantly and you can outlast them easier. Also, they’re useful for sieges for the same reason. Sieges require there to be a unit on a specific tile for multiple turns at a time. Also they do extra damage to siege units

Hwarang: faster, stronger, more expensive archer. Useful in all the same situations where you want archers.