A little yes, and a little no, anon. Let me see if I can explain.
There were definitely arcs where I felt Nick behaved very out of character. And in the Juliette/Hexenbiest arc at the end of season four, I felt that everyone behaved out of character without any good explanation (except for Juliette, who had all the reason in the world). It was almost like they made the entire team thoughtless and incompetent just so they could force Juliette’s arc, when there were definitely better ways to make that happen.
Granted, some of Nick’s writing during this time was par for the course–emotional avoidance, disregarding Juliette’s feelings, making things about him that so very were not–but the beauty of the show was that the characters’ flaws often balanced each other out. Nick’s tendency toward emotional avoidance and self-centeredness was balanced out by Juliette’s insistence on facing things head on and Hank’s tendency to point out the problems in his actions. Monroe’s pigheadedness was balanced by Rosalee’s level-headedness. The entire team’s collective gooeyness was balanced by Renard’s ruthless pragmatism…and occasionally Rosalee’s, depending on the subject. They all had skills and strengths that worked well with the rest of the team, and they were (mostly) good at communicating when it mattered.
But in that arc, suddenly, no one was balancing anyone out. No one was reacting to anything the way they usually would. Everyone was being ridiculously obtuse and not talking about shit and it was infuriating to watch. They basically all fell back to letting Nick do whatever he wanted–similar to how they acted in season 2, actually–and the end result was Juliette dead and Diana in the wind.
But overall, I thought Nick’s writing was fine in seasons 5 and 6, with the exception of one particular subplot (you know the one) in which the writing, acting, everything felt forced and stilted and just wrong. So wrong that up until the final episode I was sure it had to be some kind of spell causing him to act completely out of character. It wasn’t just that he was displaying traits that seemed unusual for him, it was that he was portraying certain emotions in a way that Nick Burkhardt definitely did not express himself, with no plausible explanation given as to why.
So. Yeah…I kinda feel you. But there were also moments that Nick felt every bit the Grimm we all know and love. Notably, his solo interactions with Hank, Monroe, and Juliette/Eve were super in-character and smacked of season one so hard that I had to swallow a nostalgic lump in my throat at times. And although sometimes his actions as a Grimm made me sad, they were also part of a clear progression that had been building for a few years, so I understood them as (not necessarily positive) character development, rather than OOC writing.