>>53299367I'm a huge XYfag but Serena's plotline was finished, not abandoned. Her story was about finding purpose in life and learning to commit to things, which she did. Even Amour was not the point of her story, her kissing of Ash was just there to show that she had overcome her insecurities and was able to take action for what she wanted.
In fact, she's probably the main companion that's had the most closed arc in the entire show. What we saw in JN was just an epilogue of her story.