Nerubian Threadmancers have been nerfed in the latest hotfix, as they no longer spam Web Bolt as often.
Nerubian Threadmancer in Delves were nightmare fuel for a lot of players, because they stood at ranged, and spammed 1M casts of Web Bolt at your face.
They were also near impossible to group up because even when you kicked them, they just stood there and looked at you funny.
Now, the latest hotfixes targets this mob and makes them slightly easier to deal with.