One concept came to mind about the Brute:
It's one of the heavy specimen, and we got 2 of those already, Scrake and FP. But those 2 already got the "speedy rage" concept in 2 different ways. Brute, with his boxer background, has his powerful knockback punches and defensive blocking. Does he really need to have the charging ability too?
If he was moderatly slow (like, the same as most specimen when they walk)and had absolutely no raging behaviour whatsoever, he would fit as a front "wall" for the other ZEDs, somewhat in a similar position to the Bloat.
I'd maybe even do something OPPOSITE to him: The more you shoot at him which he blocks with his armored hands, the slower he walks (to like, 30% slower max, faster the more damage is done to it), which then moderately fast raises up again in speed if you don't shoot at him. Then, to make sure the Firebug has some use, make him have absolutely no defense against his DoTs, and also make the Brute slow down those 30% IMMEDIATELY and for as long as he is on fire.
Meh, just some ideas