Why?
Since common sense isn't one of your strong sides: Because it would influence every singular infantry engagement if its even possible.
fist firing weapon with low accuracy have very high DPS vs light armored vehicles compared to bolt action weapons. That is a fact and it irrelevant to any other issues.
Exclusively at CLOSE RANGE. Good thing that lights are faster then infantry and have no issue keeping range.
At longer ranges burst durations, aim times and other delays make rifles vastly superior.
Don't park fragile lights on top of SMG infantry.
Again, its L2P positioning issue, not a balance one.