Channelers are the perfect example of appearances can be deceiving. Being an all-female class like Amazons, at first they are mere nuisences, being unable to do much damage. As the game progresses, they gain Sleet type spells, allowing them to freeze your units, but they are still minor threats until you hit near the end-game. Once you reach the mid-teens in levels, they start gaining powerful equipment, including the Holy Miter, which brings them back to life with half HP upon death.
They're real power lies in giving them a Talisman accessory, and the Asaya staff. the Asaya is air affinity, so it is advisable to train your Channeler as such. Given that combination of equipment, as well as an armour that boosts spell range, turns them into one of the strongest units the game has to offer. As both the staff and talisman raise magical damage, they are easily able to kill any unit in one or two basic level spells. the spell that makes them broken though is they're Combo attacks. They have short range and draw off Affinity, but deal insane damage, easily dealing upwards of 1000 damage with a Combo 1 & 2.