The Barbarossa can work, but you are correct in it being very map-dependent and underwhelming. I like using Barbarossa with Death's Head Licenses (assumed for an LL6 character). Kinetic Compensator + Anti-Material Rifle + Overpowered Caliber with Brutal 3 + and Crackshot 3 is an effective combo. Melee Barbarossa is also something you may want to try.
Viewing post in Barbarossa, How I Mourn For Thee
Immune to knockback and prone, good for holdout sitreps. It can also grapple anything. If you need it to move to a specific location, having a Black Witch as its squire, using Replulse PCP + Ferrous Lash to hit that clean rollout. Running some Blackbeard, Tokugawa, or Balor Licenses can lead to some nasty stuff. It sounds dumb, but it can be quite effective, depending on the map and sitrep. Flak Launcher and Roller Payload can come in clutch as well.