Really? Have you tried various characters of various levels? Also, if they're called "Master Vampire" They could be level 18 or level 42, as they are levelled without name change.
If it's true they're all hard then that really svcks though.
They
are leveled random attacks. It doesn't matter if you're level 5, 18, 38, or 72 (I've tried it at all of these levels). The Vamps are still labeled as Master Vampires every single time, but the abilities and the stats of said vampires are leveled to the character level.
At lower to mid-range levels, the City Guards will almost always just punk the hell out of the invading vamps. At later levels, the City Guards do have a difficult time with defeating them, but you're the Dovahkiin. This sort of stuff is what you're there for. And by the time you hit your later levels, you should be knocking off master Vampires with relative ease, regardless of how much they run around, unless we have a bunch of poor character builds floating through Tamriel...