I still say that Slayer plus ten vampires with automatic weapons equals dead Slayer.
Picture it. Buffy is hunting. She enters a deserted alley. At the far end of the alley five vampires appear. The tiniest of smiles flickers across Buffy’s lips as she prepares to fight. Suddenly she hears a noise behind her. She looks over her shoulder to see another five vampires at the other end of the alley. The smile fades, but she still knows she can prevail. Until each vampire raises his machine gun and pulls the trigger.
I’m sorry, I don’t care how fast and powerful Slayers are, they are not going to be able to dodge a thousand bullets a minute. Yes, the vampires are going to cut themselves up at the same time, but a) they’ll heal and b) we’ve seen vampires any number of times go into fanatic mode and be willing to sacrifice themselves.
Of course vampires won’t start ganging up with automatic weapons because that would rather shorten the life expectancy of the show. “I am Buffy, the Vampire Slay-” rat-a-tat-tat. “I am Phyllis, the Vampi-” rat-a-tat-tat. “I am Millicent the-” rat-a-tat-tat. And so on.