This is what I pointed out during the offseason as a very big concern. I went back during the summer and watched our games from last season and it seems like a lot of the people making game changing plays for us are gone. That's not to say we should have overpaid for any of them, but when you collectively lose a lot of players who made multiple game changing plays throughout the season, you need their replacements to compensate and that hasn't happened.
Carter had 5 interceptions (top for NFL LBs), a sack, and 8 passes defensed.
Whatever one may think about Carter -- he made game changing plays on defense last season.
Through 6 games, the Cowboys are dead last in the NFL with a grand total of 3 forced turn-overs so far.
I don't think it was a mistake letting Carter go, however, they needed to make up for Carter's production.