1) The Castle has more archers.
2) Archangels, in my opinion, are the strongest units in the game, even stronger than black dragons.
3) While the zombies are still approaching, you can shoot them down...
and it's not a given that the hero will have the Haste skill; it's not always granted (although it's often the case).
4) Crusaders attack twice, and archers shoot twice (although Vampire Lords regenerate health).
5) Death Knights are not stronger than Champions...
and archers (i.e., liches) appear in small numbers in Necropolis.