I don't need my rifle/SMG people to waste their shots firing at a Greg, I need them to protect my AT people from the spiders it summons, and them wasting their ammo on a target they can't meaningfully help to kill runs counter to that.
A "Only Shoot at Heavies" firemode would be nice too for the inverse situation, although that's not nearly as much of an issue. Micromanaging taking out one big target is easier than microing a bunch of small ones.
#Add a "Don't Shoot At Heavies" Firemode
cold marlin
Could be rolled into the "Don't shoot at structures" firemode, as a Greg and a hive are largely the same in terms of what can meaningfully help to take one down.