The Campbells were a relatively minor clan until they supported the Bruce who awarded them much of the lands formerly held by the MacDougalls.
The MacDonalds were indeed the hereditary Lords of the Isles beginning with their founder Donald who was a grandson of Somerled, King of the Isles.
My Dad won't have Campbells soup in the house as we too are MacDonalds. Not all of their Clan history is so dark however, they were Scottish patriots and loyal to the Bruce and his successors in the time our mod is set.