Didnt have time to read the whole 9 pages but just my 2 cents, It all depends on what map you are playing in, maps with many shortcuts and open areas will be dominated by lights with long range loadouts, more linear maps with choke points and obvious passages will be dominated by heavies, this is because of the lack of random terrain and the abundance of cover. The lights would have to face the heavies almost straight on. But IMO lights will win overall, just look at tf2 videos the PERFECT spy will always win against the perfect heavy, but there really is no way to tell how much agility and firepower account for, but since the Brink dev team is puttin so much emphasis on SMART movement and lights can utilize it best I believe agility will play a bigger part.
Edit: forgot about gnades that would help on choke holds and such but heavies would still have a slight adv. if they knew the sniping spots
Note: The Brink team admittedly built maps that favor uses of s.m.a.r.t. movement, so heavies will preform (gameplay wise not skill) more like traditional fps games.
L's willl get to all objectives faster and will complete objectives faster, the L's will also have access to cover that the Brink team designed specifically for smart movement, and generally in other games teams of pro snipers always win, but if the heavies use the long range loadout they will lose their damage advantage and then it will be up to who snipes better which IMO are lights