I am a Jater, However
, when he with Kate, due to Kate rough and hard core personality, I feel like Kate is the man in the relationship, and Jack is the woman. I often joke to my fellow Jaters that she probably took the guy role into the bedroom .
But with Juliet she is so fragile, yet strong and the relationship is balance, she the woman and he the man.
I never thought of Jack/Kate that way, but I agree with you that Jack and Juliet had a nicely balanced relationship.