Yeah, that's what I was thinking when seeing all the marks on the inside of the upper receiver. None of mine show marks like that. And I've got thousands of rounds through them. It definitely looks like it's (the carrier) drifting off of it's center axis. And that would make sense with the way the receivers are lining up.
As far as play from side to side, all of mine have barely enough to even be noticeable. Surely not enough to allow the upper to line up outside of the lower. I would wonder if the block on the upper, that the takedown pin slides through when closed together, isn't machined properly (wide enough). That would possibly allow the ass end of the receiver to move from side to side.
I would hope that Armailte would make this right. In the past, I would have said that there was no question. But I haven't had any dealings with the company since it changed hands, short of just buying individual parts.
I may be the Armalite pusher around here....and I love every Armalite rifle that I have. But, that being said, I'm not a blind rube or a shill for them either. Things change when companies get sold or absorbed sometimes. We'll see if they've kept their integrity of quality or not with this one.