So, by my count, we now know that the FAL, pistols, shotguns, sniper rifles, and all SMGs are overpowered. Oh, and scorestreaks, stun grenades, and explosives. Did I miss anything?
Seriously, though, you're probably experiencing some lag compensation (that does need work) which makes it seem like you're dying to one shot when in reality you're being hit 3-4 times. And the guy who killed you is probably in one of the other threads complaining about how you soaked up 8 hit markers before you finally went down.
A sniper rifle can still take someone with a FAL out.
Another assault rifle can still take someone with a FAL out.
Even from mid-range the SMG's can take somebody out.
It just depends on what you do.
I've used the FAL with select fire (and still do) and while it is powerful on range, it is very vulnerable from a close range. So just flank the guy instead of just walking in his crosshair over and over. The maps are designed so there are tons of way to approach a single position.