Thralls have started equipping throwing axes, and Javelins to use as melee weapons (not sure if this was always a thing). They have lost almost any inclination to attack. I have seen only two thrown javelins. Those few that can be coaxed into attacking will swing their throwing axe and do a negligible (0?) damage. Javelins seem to do expected damage.
Whatever changed has turned an exceptionally efficient and brutal army into a wet noodle that could be killed by a single attacking bearer thrall.
Edit: I think my problem is a collection of smaller problems compounding. Thralls were clumping on stairs because too many wanted to be on platforms. There may have also been some line-of-sight issues. Thralls with bows function as expected from non-elevated stations, without any of the derpy spectator behavior. If the change to throwing weapons was intended, notice should have been given. This is the kind of change that players should have been given advanced warning on. As it stands, there is no mention of it in the patch notes.