While a basic lmg has no unique role, maybe a gimmick would be in order. For instance, it could be a weapon with a large capacity and high rate of fire, but extremely low damage. To counter this, enemies hit by the weapon experience a wobbly and fuzzy screen, as well as a decrease in movement speed, because of the weapon's electrically charged projectiles. Enemies at a distance would not experience this effect because the charge would "burn out"(not the most correct term). This would give the lmg its own unique niche as a SAW, or squad automatic weapon, which would have to be used in tandem with a team because of its low damage.

there isn't a need for an LMG in this game. An LMG is a weapon that (in RS) normally shoots a carbine set round (5.56), at a bit of a higher rpm then what an AR can do w/ longer duration.

If you add an LMG, you'd have to then buff the damage of the HMG (which really would hit close to being OP, as seeing how even a basic HMG is nasty), and have an LMG do less damage then the HMG, but have a higher rof, which wouldn't work, as the HMG is already at 2k which is probably to fast as is.

By adding an LMG class you'd have to rework the entire HMG weapon class of damage, rof, "recoil", etc? It just wouldn't be a feasible addition to the game.