Did you forget the Steel Legion?
A few of you have commented already, asking about the Armageddon Steel Legion.
Armageddon has been at war for generations now, and the world’s original Steel Legion defenders have been worn down to a fraction of their original strength. There are still plenty of them about, though they now represent just a fraction of the expansive Astra Militarum forces deployed across the world, supplemented by regiments from every corner of the Imperium.
Fun fact. The first appearance of the Death Korps of Krieg was actually on Armageddon, in Codex: Armageddon, released in 2000. They were shown as an alternate colour scheme for the Steel Legion.