In the show and books, Jon was always the outcast, The ‘Rut’ of the litter. In the books, he has nightmares in Winterfell and he always feels that he does not belong there and so on. He is soft-spoken with a heart and mouth that Ned would be proud of. He goes to the watch to find himself and protect the realm.
He sacrifices the love of his people for the good of the realm(yes, someone other than Varys wants this) to make an alliance with Dany to win the war against the dead. He kills her queen and his aunt(as Varys duly mentions) for the good of the whole world. He does so much stuff that he in many ways single-handedly decided the fate of Westeros.
and Yet he is detained and imprisoned and sent off to the real north(whilst his brother and sister were rulers of course). I mean we deserved a better ending.
I know GRRM’s world indicates that he would never have the fairytale-Esque perfect and predictable ending as life just does not work that way but there were other ways in which he could have been utilized.
Like In ‘Deathly hallows’, we know that Harry will probably win but it's spinned-off and shown in such a way that we are always in suspense and at last although he achieves everything and although it’s predictable, it's done in a satisfactory way that’s just really amazing.
Maybe King of Westeros would have been too far a stretch but I would have been delighted if he was King in the North at the end. His whole arc him feeling that he does not belong there would have come to a perfect conclusion with this.
My personal ending for him is him dying after fighting with the Night King(We deserved that) just before Arya kills it and he dies with his siblings and Dany beside him symbolizing his love for his family and to end his life on a heroic note. What he did he deserved better than to sent off as a prisoner but sadly that’s the way it is.