system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40K] How powerful are the Imperium's non Astarte armies?

How far can you really get with only Guardsmen and their variations?
gpt
They are, arguably, more potent than the Astartes, overall. 

While the Space Marines, in their various forms, act as special forces, decisive strike teams, behind-enemy-lines insertions, and massive force multipliers for larger armies, it is the Imperial Guard that holds the ever expanding vanguard of enemies of our Emperor at bay. The Guard are almost always the first to show up and the last to leave, and you can bet they'll be bringing the pain for their entire stay. People like to poke fun at the "little" guardsmen and their "flashlight" lasguns and their "paper-mache" armor, but if they were as utterly ineffective as people like to joke, then there's no way the Imperium would continue using them to the extreme degree that they do. 

Where there are enemies of the Imperium, you will find the Imperial Guard in massive numbers, filled with zealous rage, and with the singular goal of destroying anything that stands before them, even if that means laying down their lives. They may be small and comparatively weak compared to many of the horrors that await them, but here we are 10,000 years after our Emperor's fall. 

It was not the million Space Marines that have made this possible, it was the countless trillions of faceless and thankless men and women that gloriously give their lives every single second of every single day in every single corner of this godforsaken galaxy.