You are picturing a world too idealistic for gameplay, that simple.
This is a game where movement will dominate; a light would be better against multiple people because of their ability to out flank and outmaneuver people with smaller hitboxes; a light with more skill can be more defensive than a heavy. That's the way it should be anyway.
You are clearly misinformed...
Movement will not "dominate" in this game. If that was so, then everybody would pick Light, Mediums would be underplayed and Heavies would just be a waste of memory - This isn't Mirror's Edge. If anything would "dominate" in this game It would be having a good aim, having good situational awareness. All the backflips, slides and flanking won't matter, if I kill you regardless.
this next part is important boys and girls, so pay attention: BODYTYPE = PLAYSTYLE. Each body type caters to different one, and there is no "best."
If you understand the proper way to play a body type, and utilize their pros to the fullest and avoid their cons, then you are doing it right. Brink is not going to be a game where if you master a specific body type (in this case, Light) then you will be untouchable and dominate every other player on the battlefield (that isn't Light.) It is also not going to be a game where if you do not master one aspect of the game (in this case, movement) then you will lose every time. You also totally disregard that classes, abilities and loadouts will have a much greater effect on how scenarios play out, than bodytypes do.
It's just my two cents, and from previous games, having a heavy type character is either op or up, and usually its up because a smart dev will reward the harder, more skillful class to play (light).
(sigh) Here we go, the
"Lights take more skill to play than Heavies" argument - this thing has been done to death. Riddle me this Batman, If Lights are so much "harder" to play, then why do they appeal to so many players over Heavies? Don't you think if they were that hard to play, more people would be opting for something (in your terms) "easier" (Medium) or maybe even the "easiest?" (Heavy) Do you really believe the Lights popularity is because players are thinking to themselves,
"if I master this harder to play class, I'll get better rewards out of it in the long run!" - sorry, but I don't think that is their reasoning behind it.
The Lights popularity is attributed to pop culture. Whether it be games, movies or comic books, the light (or medium), agile fighter, tends to be the hero or the popular choice. Even in instances where a Heavy is the main character (like a Hulk or Juggernaut comic) \their popularity is usually dwarfed by Lighter, more agile comic book characters. Look at the characters in games - Sam Fisher, the guys in Assassins Creed and Prince of Persia (never played them,) Link, Mario, Master Chief, Ryu and Ken, Ninja Gaiden, Simon Belmont, The characters in Mirror's Edge, Samus, Mega Man, are you seeing a pattern here.... For Brink, a light, agile "sneaky" character + Sniper Rifle, knife, smg and/or Operative class (spy or rogue) = appeals to a lot of people, regardless of how "hard" they are to play - it all comes down to a "cool" factor. Yes, there are players that want to use Light because they excel at that playstyle, but if all the people who want to play Lights, want to do so because they are good at it (in polls, Lights have around double or more the appeal than Heavies) then Lights really don't appear to be that hard to play at all. In fact, (based off current trends and polls) The Heavy, if not the hardest to play, will be the most valuable, due to their scarcity.
In music terms, Light's are like guitar players - they are a dime a dozen. Due to their abundant supply, finding a good one is just a matter of time. Heavies are like singers or drummers - They are the hardest to find because there are so few of them, so finding a good one can be even harder.
Your explanations and discussions are so one-sided, they are laughable. The bottom line is this -
to you, movement is key and
to you , mastering it is everything, most likely, because it compliments your playstyle. Movement means nothing to me, because I'm going to be hangin back with my homies, buffing and healing, and providing support, because that's how I enjoy playing, and what I am best at. So you can master all the running and jumping you want, because when you come in the direction of a Heavy, pointing a minigun at you the size of a tree trunk, that has a 200 round magazine and fire faster than you can run, then in the words of Trinity, "Dodge this."
Oh, and the flanking argument is dead as dead as well, since a good Heavy will either be watching his flanks, be in a place where teammates are watching the flanks, or position himself where flanking is increasingly difficult or impossible. lol, it humors me how in all these "Light vs Heavy" scenarios, the Light is always an elite, trained assassin, the Heavy is just some big, dumb, idiot with a gun.