I doubt Ren will bond with MC. She is far too arrogant and egotistical to be able to harmonize well with Noel, Cia and Amy. I can see Noel getting along with her because she is a sweetheart, but Cia and Amy will hate her when they see her true self. She will most likely end up being defeated and going back to her castle or bond with Clara.
Although, I don't think that combo will be stronger than MC because of Clara. Ren is strong because she herself is controlling Clara body, but if they bond, then no matter how strong she is, Clara won't be able to keep up. If she could, she wouldn't even need Ren, Eda was already more than strong enough to beat down Unus without breaking a sweat. Still, I hope this incident makes Clara start to train and get stronger. Its a waste to have Eda, a martial arts master, as a Dark One and not be able to use her powers at all.