If A/R takes 3-4 rounds to kill and a sniper rifle takes 2, then the rifle does, in fact, kill faster. It just doesn't give snipers insta-gib rifles so they can run around at point blank with rifles instead of selecting all class automatics.
Not really since a true sniper (ie:bolt action and not some VSS carrying wannabe 😀) has to work his bolt to before he can even take that second shot, meanwhile the full auto assault or engineer has sprayed 30 rounds all over creation.