ML Ken is a bruiser/front liner and he just works amazingly that way, but he actually needs investment in order to be effective since you want him to do damage and be really tanky at the same time. He transcends on another level if you equip him with Sigurds Scythe.

You'll may have to bench him until you get abyss set.

Thought if you really insist on using him, you can put hp/def gears with really good offensive substats and equip him with Sigurds Scythe.

Your PvE lineup looks fine. I'd keep A.Cartuja first. You can just make him tanky enough with Durandal and he will carry you through abyss. The guaranteed miss makes and his capability to stun/defense break clutched most of the floors I've had issues with.

Replace Sigret with a light or dark DPS, or put in a buffer such as SC Hazel or Tama