Statistics, are mostly misleading, and almost always over-used, and over-valued.
A couple of scenarios: Some teams give up too many yards, are reasonably easy to run against, but get bailed out by causing/receiving an inordinate amount of turnovers. (Like we were last year). Does this mean that the team is good defensively, or just the beneficiary of a large number of lucky breaks? We caused most of these turnovers last year, but we all know that very few teams do this two years in a row.
You could rank a defense by how many points it gives up over the course of a season... but this too, is somewhat misleading. For instance, a low scoring team, or a team that runs the ball a lot tends to shorten the game, with the opposing team dialing back their offense and playing the possession game-- running the clock, rather than the offense.
So... I believe that the real ranking of a defense comes down to how it does vs. elite teams when it absolutely, positively has to stop several drives in a row. But, yes... this is almost impossible to measure.
So that brings me back to the Original Post and it's question...
I can't give you an answer, because any answer that it generates won't really answer the question of whether our defense is good enough.