1. no, low damage does not make a gun crap. Just takes more skill to use.
2. no, only has low useage because it is a harder gun to use.
3. no, the recoil can be compensated for if you learn how.
4. Iron sighs yes, red dot no.
5. No, win more fights with it than ACR.
There are no bad guns only players that do bad with them because they can not learn or adapt to how the gun is meant to be used and try to push the gun beyond its area of performance.
You do realize that a gun can not be utter crap if somone is rocking a lobby with it. Just because someone tries to call it crap does not make it so. Just the person that tried using it and failing and thus thinking it was crap was crap at using it. There is a big difference between the two.
There are a number of reasons one might "rock a lobby". It may just be you're a better player than you give yourself credit for.. or maybe the people you play against just aren't that good. Back in CoD4 before it was popular, I was placing top 3 overall in matches running a knife only kit, many times winning matches. This was before the knife was made to be really good.
Doing good with it does not statistically make it a good weapon. It just means you're able to overcome it's various weaknesses. As someone else said earlier, just because you can beast a lobby with a USP .45 does not mean it's a great weapon. It's inferior in almost every way to most AR and SMGs. But it is possible for a player to do really well with it.
I myself have used the AK47 a bit, and while it's by no means a "terrible weapon" or weak, you can't argue facts. The facts show that the majority of the other Assault Rifles are simply a better choice. It's RoF, Recoil, Raise Time, and Reload time simply do not work in it's favor in comparison to other weapons.
Can it be a good gun? In the right hands, sure. But statistically, there is no reason to choose it over some of these other ones available at earlier levels.