Necropolis or Castle (Which one is stronger?)

It's hard to prevent this, the castles need to be close together. And to prevent this gathering of death blossoms, you need to eliminate the Necromancers immediately.

The problem is that on large maps, castles are rarely "very close" to each other, and even more so if you're playing on 200% difficulty with strong monsters... when there are hordes of enemies all around. Even if you see them in the first month, getting to them won't be that easy.