Well, Bethesda quietly removed the vampire attacks from SSE after player complaints.
My belief about the vampire attacks from the start were just a way to encouage the player to do the Dawngaurd quest line. It added a sence of urgency to the player. For me, though, it conflicted with the "do whatever you want" style of gameplay.
Do you want to do the "Blood on the Ice" quest? Well, you better complete Dawnguard first; otherwise, Master Vampires will slaughter all the NPCs.
The vampire attacks are stupid when you think about it because the solution is simple: lock down the cities at night. With guards patrolling outside the towns, there's no way a few vampires and thralls could make it into town. All of the fighting should have occurred outside the town.
Balgruuf locks down Whiterun over dragons that can fly over the city walls, yet he leaves the gate open to vampires during a rash of vampire attacks. Must be a Democrat Jarl.
I complain about the story in Fallout 4, but this is right up there. I could also rant all day about how dumb ALL of the vampires are for believing the prophecy would benefit them, but I'm too hung up on the gate thing.