i think they add a nice bit of diversity, since after you get any armor (even wooden lamellar) the rock throw that drifters does the same damage as a light breeze. Also taking into consideration that all you have to do to counter a bowtorn is run up to them and they run away. (plus drifters are really slow, but if its shivers that are chasing you i can see how its a different story). Bowtorns can also be kinda cc locked with bow spam aswell. But with all said i can definitly see how a mob of them can be a real pain to deal with.