It would be interesting to learn what experience Kirk has had of Klingons outside and before the onscreen events. Garth of Izar refers to past military glories, which Kirk sounds embarrassed about, as if he himself once indulged. Was that against the Klingons?
Does Chekov know how Klingons smell, or is he just quoting a (true) rumor? Kirk at that point apparently does, having met Kor in rather heated circumstances...
The ending of ST5 isn't the part that IMHO creates a discrepancy there; from the looks of it, most of the Klingons in that party still hate the humans, and most of the humans still fear the Klingons. It's the ST5 Klingon character of General Korrd that represents something of a discontinuity, as the old wardog seems to have Kirk's sympathies and vice versa. But that's individual Klingons, and while Korrd may actually be a fairly typical example of Klingons of his age and position, the mass of young hotheads that Kirk would typically deal with would outweigh even the portly General!