His relationship with FP had development, it had nuances and interactions with the established cast. There was a dynamic there with her alignment and an interesting dilemma with Finn trying to justify/help her. But they threw it away in a single episode because finn wanted to hear a message ABOUT THE FACT THAT HE FUCKED UP THE RELATIONSHIP BY WANTING TO HEAR THE MESSAGE. How the fuck did that even work? If the cosmic owl didn't tell him he fucked up, he would've very fucked up/
And even, It would've been so interesting to see finn deal with the fact that he was practically a part of an evil family. It would've been nice to see Finn mature and deal with the complexity of the very black and white nature of good and evil in Ooo mashing with familial bonds. But instead we must be complacent to the fucking Status Quo
I'm glad they didn't give him a love interest this season because I know they'll fuck it up.