Neither one is stellar defensively and Turner has had a knock on his defense (which I believe to be unwarranted) but to claim that Difo is superior or "significantly better" than Turner based on freaking "metrics" is just freaking stupid and again confirms that the likes of Slateman and company do nothing but parrot what geek stats tell them to say.
Is this another instance where we are going to need Slateman to define what "good" and "average" mean? 
Like I said before I don’t understand the defensive metrics so I don’t quote them. It’s sort of like a black box to me.
That being said if I look at the fangraphs defensive leaderboards, the Name at the top for the Nats is Taylor, and then Severino and Rendon, which makes me think there is some validity to it.
The one I saw was Defensive runs saved which for this year Has Turner at 7 and Difo at 5 (I combined the SS,2B and 3B time for Difo
I think they are both fine defensively, but neither will make you forget about Andrelton Simmons.
As far as Spider’s general rant, while I think the defensive metrics aren’t perfect, I appreciate that there is some attempt to quantify the quality of defensive play beyond the eye test or people’s gut feelings.
As much as it pisses off spider when people “parrot” what they hear, it pisses me off when people make assertions that have no basis in any data. That’s how we end up stupid crap like people saying Derek Jeter was actually a good shortstop...
That being said, I believe Turner is a superior baseball player to Difo. And Turner is going to get better. He has a total of 260 games under his belt.