One of the forum member put it succinctly this way: there are too many Cliftons for one show. It is bad for the other pros' morale, especially when some of the Cliftons behave in a childish, unprofessional way (it was discussed on other threads).
At the very beginning, I liked Joanne, tolerated Karen, could not stand attention-seeking gurning Kevin.
My opinion changed when I saw how good Karen was in Latin dances and how jealous was Joanne of more successful SCD professionals.
I have also changed my opinion of Kevin who has become more restrained and elegant this season. I like him and his partnership with Louise very much. I also saw a couple of interviews in which he looked much more intelligent than Karen and Joanne. Karen, on the other hand, did not look or behave too smart. She was clowning like a not very intelligent but spoiled kid - a huge turn-off for me.
I also cooled toward Joanne. The hype around her choreography did not convince me about her talent: yes, she knows how to use the entire floor but she also overuses props and inserts unnecessary theatricals that look like a cover-up for her lack of choreography skills. Besides, I am not sure that the above-mentioned hype was not artificially created by Joanne's parents (who, being part of the dance world, quote probably participate in these forums) or even Joanne herself. After all, she engaged in Twitter wars with her critics in the past... Joanne is a weak Latin dancer; she is good in Ballroom, but I still prefer Erin and Natalie. (It's just a matter of taste, obviously: I love statuesque ballroom dancers.)
To conclude:
One or two Cliftons would be quite enough for SCD; three is overkill.