Definitely room for improvement but I think "mediocre" is overstating it. We've never had the kind of talent and depth in the DB room as we have now.
I could be persuaded to lower that to a B, but he's had some really good games and seasons overall.
In order for BYU to take another step forward as a program, I think the defense needs to improve a bit, especially along the DL.
But he's also never been responsible for major issues either.