Crystal Soul Spear doesn't seem to be hardly putting a dent in these on regular NG (ascetic Freja for the spell). Using a +10 magic infused Witch Tree Branch and 50 Int. I'm able to down Alonne Knight Captains with a single spear. Hexes might be the go-to magic here according to some of the comments below.
I can’t believe that these enemies only drop their unique sword, not the battle axe or halberd. It even says that their weapons were forged by an artisan, but they drop normal weapons, that’s just lazy design.