? You do know that assassination is merely killing someone suddenly or secretly, especially if they are prominent?

I guess you didn't read the section where Semirhage personally went and assasinated various royal families? It is obvious that the Forsaken are in a superior position to assassinate people because 1) they can channel, 2) they can channel exceptionally strongly, 3) they can Travel, 4) they can use T'A'R, and 5) they are powerful enough to kill anyone who gets in their way while covering their tracks very well. Heck, Semirhage isn't even a noteworthy killer, and she accomplished her assassination of a heavily guarded noble family in a few minutes with noone knowing until she had already left and gotten ready for her afternoon tea. Plus, with balefire, it is obvious that when you want to perform the ultimate assassination, only a Forsaken or darkfriend channeler can accomplish it. We've seen Lanfear and Moghedien commit enough murders on-screen that I don't know why you doubt that a Forsaken wouldn't kill anyone they saw as getting in their way - especially to establish cover identities.