Genzin would fit in quite well - he can do the AOE DEF down, and abbess finish off with her A3, and he can also do a single-target nuke to get through unkillable. Just be aware that since his A3 ignores shield, it also doesn't strip shield, which means if he doesn't finish the target off, it'll be harder to kill than you would otherwise expect.
The last piece that would really be helpful is someone with an AOE TM manipulation. You want to put Abbess and Genzin in pure damage gear, but in order to do that, you'll probably need to reduce the TM of their team so that they can act first.
Have you got anyone with good AOE TM, or perhaps even AOE stun or sleep? Rhazin would be the "easiest" to get since it's fuseable, but there are plenty of others (Nethril and Big'un come to mind).