It was mentioned that Thorakitai were armored warriors, and in Infinity the Thorakitai do have ARM 3. However all that protection slows them down, and their MOV is 4-2. While that looks bad on paper, a majority of Orders are Move + Skill (usually shoot!), so the 2 rarely comes into play. Just watch out for Difficult Terrain! But when hoofing it across the battlefield, that 2" deficiency can add up.
The Combi Rifle Thorakitai can be used as a basic grunt or as an Engineer.