How should I develop my units to defeat a Knight?

Mish-gun, it seems you've stopped contributing to the topic, or are you waiting for the final version? Here's another advantage for Necropolis – you can conquer Utopia with just vampires and without any losses. About 70 of them will be enough to eliminate any number of inhabited dwellings.

Most likely the latter!
Regarding conquering Utopia with 70 vampires, I agree, it's quite possible!
Actually, I conquer Utopia without any losses anyway – 4 angels and 15-20 knights!
Necropolis just does it earlier!

Regarding Anti-Magic – Haven without Anti-Magic is like Necropolis without Dominate!