Think about it.
With a LMG you've got no choice but to hose full auto... and with that rate of fire each little shot shoots (estimated) 6 or 7
With a AEG you can chose either semi or auto, But the ROF is substantially lower. I know with my M16 when I'm in auto I can fire a single shot with a slight trigger pull...
IMO the 350 Limit is a smart move. No one wants to be hosed down by multiple LMG's when just one BB would do it.