My understanding from old articles and tumblr discussion is that Adalind was never supposed to be a long-term character. She was basically written in for a few episodes in season one, and then they liked Claire so much that they wrote more for her.
Which I get. What’s not to love about Claire?
But then they didn’t really know what to do with her. That’s nothing I heard, just an observation. They had no clue.
She spends most of seasons two and three “meanwhile in Vienna,” then comes back in seasons three and four only when they need a stronger villain to make the plot move. They spend very little time developing her but put a LOT on the character’s shoulders.
I also don’t think the writers necessarily wanted or planned to put Nick and Adalind together until a vocal minority of fans began demanding it. They certainly failed to set it up at all in seasons one through four if that’s not the case.
Then once they got together, Adalind became a background player for the most part. She got one or two good episodes in seasons five and six, but those were all when she was stuck in the mayor’s mansion with Renard. Otherwise, she became a very passive character with little agency after season five.
Even the single “I love you” Nick ever says to her happens in the Other Place, in a reality that gets erased. As far as Adalind is concerned, it never happened. And that’s where they end the show.
Looking at all of that, I honestly can’t believe they planned or wanted that ship to happen. Which begs the question: why did they never fix it?