I agree with all your points, except the very last. In book 6, the relationships absolutely take center stage... to the detriment of the story. It almost feels like JKR is responding directly to the fans: "Hermione/Harry? NO! Ron/Hermione! Harry/Ginny! Lupin/Sirius? NO! Lupin/Tonks!" And while she left gaping plot holes (when exactly did everyone learn that Malfoy had a hand of glory?) she goes on for pages about teenage toungue kissing.
The coupling (to my mind) was relentless. I mean, please. Filch/Pince? What's that all about? Meh. Well, to each her own, I suppose.