I have a team of three guardsmen and they're all legends in their own right. Each of them is making anywhere from three to five shots a turn.

The Guardsmen class by itself is fairly OP, but if it bugs people, they should just get "More enemies" mods like the 25-50% or the 75-150% mods. The guardsmen will allow you to walk out of fights without squad wipes.

I'm honestly slightly impressed you got 3 guardsmen to high enough level to get that many shots a turn.Unless you're running hidden potential or not created equally, Guardsmen have lower health and aim than almost every other class until they cap.

Can I ask what difficulty you're running on and any major difficulty adjustments you're using?

Sorry that this is so late, it never said there was a reply and I took a break from XCOM. Thinking back to back then, I was the 75-150% more enemies mod with a Spark in my squad, so it's rocket was probably giving me enough kills consistantly to get guardsmen up the ranks quickly. On top of that I was using no rank up throtling, so one mission could theoretically give me 2-3 ranks each depending on the number of enemies and kills. As for the difficulty of the save, I was running it on commander.