again, they got money for Chewie to play the Operative and so we didn't get Jubal. now don't get me wrong, I <3 Chewie, especially in Children of Men, but man, just cause you gots the money don't mean you gots to spend it in places that don't matter. Jubal would have rocked!
Perhaps he would have, but he was the wrong character for this story. Serenity
the movie needed the Operative, not Jubal.
Jubal was insane. He took the job as an assassin and bounty hunter because he was distinctly unstable and it gave him an excuse to hurt people, not because he had any feeling or loyalty to any particular cause.
The Operative was completely stone cold sane. He knew that he had to do horrible things, that he wasn't a nice person because of those things he had to do. But he had such belief in the rightness of his cause - the Alliance - that he considered any unpleasant means to be worth the end. He did the things he did because he wanted the final result for the entire known 'Verse, even if he himself was not allowed to be a part of that 'Verse because of the things he'd done to achieve his end. In short, he was a true believer, not a paid mercenary.
And that's important for the story, because at the end of the story the Operative loses his religion. He discovers that the Alliance is not the faultless perfect state that he believed it to be, and he must basically reconstruct his personality from the ground up because of this realization. Which is the same thing Mal had gone through when he lost his belief in the Independant army - and "God," however he defined it - after the Battle of Serenity Valley.
We see Mal, through the course of the show, rebuilding his life and finding a new reason to live - his new family on the Serenity
. In the aftermath of the film, the Operative must now do the same.
Jubal Early couldn't have offered us anything like that. He would have just been "kewl."