In (minor) defense of loose character threads, it's kind of difficult to keep consistent characterizations over 15 season and 4 show runners, all with different visions of what the characters should be and an acute awareness that the plug could be pulled at any moment. What even is Cas's character arc anymore? He had an extremely tight arc in the Kripke era, and became self-actualized by the end of S5. Cas was the only angel to stay loyal to God's commandment that they should love and protect humanity above all else. He learned to question the authority of his superiors when he realized their agenda contradicted the will of God. He lost his faith and fell to nihilism during a fruitless search for answers, but found solace in his shared experiences with humanity and came to love them. And he chose to fight and die by their side in a hopeless war, not because it's what he was told to do, but because it was what he wanted and decided for himself. That's who Castiel was: the one loyal guardian angel of humanity who forsook his brothers to do what he knew was right. And he was rewarded for that decision with resurrection. What a great story!
But since then there has been all of this stupid back-and-forth about who's side Castiel will chose (that was definitively decided in S4), about how he lets his ego and naivete blind him into making world-endingly bad choices (even though S4-5 Cas was smart enough to see he was being used and made the right choice), about how he's endlessly looking for redemption for said bad choices (but I guess maybe he's given up on that now?), about how he's slowly becoming more useless to the Winchesters and has developed a complex about about it (this is just character assassination), and now he's inexplicably daddy of the year and consequentially more human-like than he's ever been, not because of natural progression of his character but because magic injected him with feels. Where do you go with that?