The only reason you'd want to replace Asajj with Han is if you want to do less damage. His damage is capped, her's is not. I use her and she's able to knock the tank down with 1 AoE after a couple of turns. I use Asajj under a Boba lead for the 50% critical damage and 10% critical chance. I only have offense mods and a couple of tenacity mods on her. Ends up doing over 175k with each hit. I think she'd be amazing in Phase 3, but tank kept blasting and killing my team before I could see just how much she can do.