Ha! You're not alone with that CountMRVHS, in not having completed the RK campaign I meant.
I played the RK more than double the times I've played all other factions combined, but never have finished the campaign. Not, because I liked other factions better, but because I don't like the late game, at all, in all TW titles that is. It might sound strange but my goal is mostly to expand to natural borders and then stop expansion altogether. The next focus is to keep all other factions alive and active, which means that they need to maintain a certain amount of provinces in order that the AI actually does something besides moving one or two stacks from a to b.
To achieve that I usually have to break all alliances and build up more or less good relations with every faction in order to be able to ally on the fly with threatened factions . I project my power over considerable distances, which is a bit tricky when I want to have generals in command of my army because of the supply trait.
Sadly, most of the times, I failed to save the rebel dwarven fortress next to the sea of Rhűn. But two times I managed to save and contain them for the rest of the campaign.
I guess most of my campaigns I gave up when either a faction got utterly defeated and whipped out or when the battles holding off Harad turned into several hours of bridge crossing battles per each turn.
I'm curious how such an approach might work out on the full map with even greater distances.