Future BiS Team Question

>! So Linnea is basically going to be Zibai’s new BiS in 6.5. I am confused though. I already have C6 Illuga and C6 Gorou, so who would she replace then if she’s at C0? Or should I keep Illuga and Gorou since they’re already at C6 because Linnea requires vertical investment to replace either of them at C6? !<