Also, the reason that she ended her relationship with Steve has been clearly identified as to protect him from harm. There is no evidence for another reason at this point. Every member of the League knows that he means more to her than a friend as well. Which makes me genuinely wonder what the hell Clark is doing.
Bones and Booth I give you, especially since the ep where their halloween costumes are Wonder Woman and Clark Kent. LOLBeckett/Castle is more analogous to Superman / Wonder Woman, as it's two adults who happen to have worked together, with expertise in different fields, who after a time find themselves in a relationship. As would say Bones/Booth.
But Castle and Beckett is Steve and Diana. She is the cop, he is the writer. When they go through the door, she goes first. Rick's a pretty good shot but Kate would have it all over him in a fight from what we have seen, and besides he often does not have a gun. I am wishing for a scene where somone asks him why he never bothered to keep asking for a gun so he can say something like "Why do I need a gun when I have her?"
Her interrogation skills [getting to the truth] are better and she can drive like a she-devil. A recurring theme in the show is that Rick is putting himself in situations way over his head, but of course he does it to keep up with her.
Damn, now I am going to have to go watch a few episodes! I hope Monday night has a new one
[For the record, the EverQueen actually prefers Bones to Castle. We tease each other about it a lot ;) ]