So I thought about the Marauder, and what I was thinking last night as I chose each armament.  I had intended for it to be able to counter smaller faster Frames with its Advanced Rotation System and Shield Focus Array.  It can focus all of its shield power into one direction and lock it onto an enemy, say that it is circling the Marauder.  Its rotation system helps it keep track of a target moving around him.  This keeps its Grappling Claws, Autocannon, and pistons lined up with the target, in theory?  Coming in close to bash on his enhanced Shield opens them up for a flurry of attacks from his Claws, Cannons, and Pistons, I would think. 

I could rewrite his Flash Skates to allow him to make evasive maneuvers for situations like that as well.  So he can still be fast, just not as fast as a Frame with less mass. 

Also, melee-orientated Frames might have to deal with the back spikes if they're not careful--they're not small 'bumps' that you brush up against and shear metal.  We're talking multiple impalements in different parts of the body if Julian times it just right.  And then they get electrocuted....

Granted, if he's ever in a situation where he's dealing multiple smaller faster Frames at one time, he's just as screwed as anyone else might be.  And that's a matter resolved by proper tactics and team strategies, right?