How should I develop my units to defeat a Knight?

You’re being pretty harsh. And do you think there aren’t enough Necromancers? Knights are slow, and there aren’t many places where they can really spread out. There aren’t any artifacts yet that help against Subjugation and Blind. And Antimagic won’t save you against Vampirism. Besides, cavalry doesn’t really cause me any problems. Angels, yes, but not knights. And as for Antimagic… well, once the knights get going, that’s it. And I’m also short on money. Try playing against Kaspar on the Outlands map and see how many knights you can train.