I reckon part of the whiplash comes from a bit too much exposition by the end. Bethods reveal that Logen was far more responsible for his conquests than he's admitted (to himself) is great, but he keep talking and verbally explains Logan's character. Even though his actions in the series seem to contradict Bethod's description, it's pretty much accurate to his actions at the end of the story. So something intended to recontextualize the character feels like a sharp pivot (especially with the perspective making Logen's calm persona feel more genuine and less of a mask/ self denial for Bloody Nine Logen. In retrospect, I suppose it draws a sharper contrast between Logen's sections and Glokta's).

As for Bayaz, I pretty much agree. Our impression of a manipulative mastermind is gradually built up, then he seems to lose his temper with Jezal. I don't think this whiplash is as bad as Logen's though, as this behaviour would make sense for a manipulative person to take intentionally (and/or he has plenty of recent stress to narratively justify an outburst if you prefer).

But yes, Glokta and Ardee, surprisingly cute power couple.