The AK-12 is the 2nd slowest auto AR, Remmington is slowest.
So generally an R5 wouldn't outgun an AK.
In my opinion, there's really no OP guns in this game. It feels much more balanced than previous titles. There are absolutely best opportunities to use specific weapons, but I have no problem with people playing with any gun. In fact, I'd rather see a larger amount of ARs like the AK-12 lying around after I kill a few people, gives me a better option of secondary to pick up when needed.
I feel instituting "nerfs" to weapons pushes people away from that weapon, just by the fact there was announcement to say they are adjusting it. A lot of the time they are not huge changes, but it definitely affects the numbers using the weapon, even if the adjustment is minor.