In the end, the zombie vampires chose to take Klaus's blood.
Excluding their queen, there are 4,500 of them in total, and the weakest among them is at the Sovereign stage. Even so, they have 45 Void-stage experts, 955 Ascendents, 3,000 Transcendents, and 500 Sovereigns.
This means that the moment they take Klaus's blood, they will all become terrifying. Klaus gave his blood to his friends when he was a Great Sage, but they all advanced from the Sage stage to the Ascendent stage.
So, he had no doubt that even the Sovereigns would become Ascendents, since Klaus himself is now a Transcendent.
Then again, there are the Transcendents who can become Peak Ascendents or even Void-stage beings, and if that isn't enough, there are the 955 Ascendents on track to become Void-stage beings.
Naturally, the Vampire race will be made up of warriors so powerful that when they appear on the battlefield, all hell will break loose.