I've many times gone back to the pages of the intro rulebook that detail those categories, and squinted at them until I get a headache. To me, all the confusion WRT those two Trooper-like categories looks like it revolves around one simple error: the Grasshopper is listed under "Skirmisher" and the Dragon under "Brawler," but if you swap those, the categories make a whole lot more sense.
The Enforcer and Grasshopper look like they want to get close and mix it up, fitting the more common interpretation of "Brawler," but are distinguished from "Juggernaughts" by being a step or two more mobile and having significant investment in what can be called long-range weapons by Intro-tech standards, which reconciles the apparent conflict between interpretations of "brawler." Meanwhile, the Hermes II and Dragon are another notch or two faster and have relatively light abiltiy to dish out and/or absorb damage, perfectly fitting a more common interpretation of "Skirmisher" by emphasising both leg reach and arm reach over the "heavy" feel of the Enforcer and Grasshopper.