Landsknecht as a standalone attack unit is horrible. But in Trebuchet-heavy strategies it could turn out to be quite useful, because it replaces the role of Maceman as a melee counter and is cheaper. After Trebuchets have done their job, Landsknechts shouldn't have problems with crippled Longbows. You do need Crossbows or Longbows in your stack to protect the Landsknechts from enemy Crossbows. But you would also need them when you were using Macemen.