The Cardinals are not an especially deep team, and they are old as well. They are currently getting several performances that defy projections and expectations of those players. I expect injuries to hit some of those older performers soon enough, and a few of the guys who are tearing the cover off the ball will come back down to earth.
O'Neil was looking terrible before he got hurt. Not sure if he had some sort of nagging thing that was affecting his performance or not, but I don't know if it is necessarily safe to assume that he will look like last year's version when he comes back. His all-or-nothing approach already made him a prime negative regression candidate this season. It is simply possible that, like Hiura, the league has adjusted, and what we are seeing now is close to what he truly is.