Reality behind the fiction? Since when has "Castle" been that? Would the NYPD actually allow a mystery writer to evolve from shadowing one of their detectives to becoming her partner? I don't think so.
Verisimilitude doesn't require that something be actually real, just that it feel
real -- that it makes it easy for the audience to be willing to suspend disbelief. I've told you over and over that the show's first two seasons had a much more believable approach, which set my expectations for the show, and that it disappoints me that subsequent seasons have taken a cartoonier approach. If you disagree, fine, but we're here to review the show, not each other.
And like I said, the Nikki Heat books -- the ones that Castle's supposedly writing within the show's universe -- have a lot more verisimilitude and believability than the cartoony world of the show these days. And I think that's getting it wrong because it doesn't fit the character. Castle is someone whose books should be broader and less believable than the world he inhabits. That's in keeping with his character, and character is the most important thing. If the approach to the show undermines the integrity of the characters, then the approach is flawed.