LMG's should be very inaccurate when firing from a standing position but I think when crouched(better if they had an option to deploy the bipod for further aim improvement, which should take a turn) they should be at least as accurate as burst fire on a rifle if not more so.
Currently my my LMG guys are my best troops by far and get most the kills, so yeah the other weapons should be given some advantages that would make them more useful. Higher accuracy on the move, and much better mobility for the rifle man and assault guys are a couple of the obvious choices.