You would think so but it's just the fact that people need something to bitch at. If they weren't bitching about the FMG they would be bitching about something else, probably the next most used weapon.
As for being balanced, a game will never be totally balanced, you would need the cover on the map to be absolutely identical, you would need everyone to be using the same gun and attachments and the enemy team would have to be at the same skill level as your team mates. Lets face it, COD, and all games would be boring as shit if they were totally balanced.
Yep. People bitched about Type 95 and the occasional uav whhore crying about Assassin cancelling out is easy mode Support UAVs.
People also don't realize everybody doesn't think the same way. Most people get teir asses pwned running around the map so they rush even if the enemy doesn't camp.
People have this ridiculous notion that online players are of equal skill levels and should play the "right" way. I rush now, but 3 years ago starting on COD I was a camping, hiding noob since I didn't know how to play. COD community love to cry though. They would rather ranr and ask for nerfs instead of overcoming obstacles and discussing issues maturely and rational.