I'll repeat myself again that the fourth game is completely uninteresting, I have no desire to play it after the third, and because of this factor, I didn't play the campaigns either, I only started playing some campaign in the LOTR add-on, but I got tired of the fourth one quickly))). My opinion is that it should be done in the third game, because fans will want to play it there!
P.S.: and by the way, could we create some kind of storyline from this campaign? We're not offering enough options, and if we've already started, we need to finish it!