I hate to say this but I have to.
If you look at the number of yards and big plays given up by Diggs this season, he'd be considered one of the worst CB's in football if not for the eight picks. His ball skills are perhaps the best in the NFL, so that's really what makes him such a threat to opposing offenses. But if he can't make a play on the football, it's a near certainty it's a big play for the other team.
Again, this isn't a criticism of Diggs, since he's basically a wide receiver playing DB and I've never seen a Cowboys corner attack the football as well as him in my lifetime. I was just a toddler when Everson Walls was picking off the entire league.