Magni wasn't more evil than Thaurissian lol. Thaurissian kidnaps Moira to hold her hostage from Ironforge, Magni has him assassinated, because he still believed Moria was a prisoner and not his willing wife.
Not to mention Magni later spent two expansion communing with Azeroth to save the her from the Legion, the Old Gods and the massive hemorrhaging of her blood across the surface. This is in comparison to Thaurissian who made a deal with Ragnaros, putting the Dark Irons into his service.