Defensemen who can play the minutes Girardi plays are pretty rare these days. To play the minutes-to play physical and to make very few trips to the penalty box--to play with assorted hurts but miss very few games. To be always out on the ice against the best players in the league. That's dependability. Coaches love dependability. He is our best right side guy and good right side guys are harder to find than good left side guys. Girardi might not be quite on the level of McDonagh or Staal but he is still very very good.
As for the notion that he plays worse with Del Zotto--that's not just on Girardi--that's on Del Zotto too. The better defense partner you play with the better results you should have. McDonagh and Staal by the way both love playing with Dan.
Statistics don't always tell the whole story. Sometimes I think people already have their conclusions and just need to find and arrange the evidence in the best way that supports their argument.
I want to address your last point first, that definitely happens way too much and I think it is one of the primary reasons that many people are big sceptics of statistics.
I want to emphasize that while I do believe in statistics, I try my hardest to not work that way. I always try to provide the correct context and I would never consciously hide a statistic that disproved my point.
Regarding Girardi and his dependability, I think there is a lot of confirmation bias hiding his true value.
Yes, Girardi has seemingly handled first pairing minutes well. But a vast majority of these minutes were with McDonagh/Staal. When we look at them apart, as shown in the linked post, Staal/McDonagh improve while Girardi suffers. That is an odd outcome if Girardi is our best RHD, wouldn't the results on both sides of the equation suffer if Girardi was better than the other RHD's?
And I don't doubt that they enjoy playing with Dan, he always gives his all and is good at the obvious defensive plays, hits and blocks. He is likely our best RHD at preventing goals when the other team has the puck. But he is probably our worst RHD at preventing those types of situations. In the long run that is more detrimental than a defenceman that has some misplays but on the whole allows a lot fewer chances.
I'll post the famous Dave Tippett quote:
"I'll give you an example. We had a player that was supposed to be a great, shutdown defenseman. He was supposedly the be-all, end-all of defensemen. But when you did a 10-game analysis of him, you found out he was defending all the time because he can't move the puck. Then we had another guy, who supposedly couldn't defend a lick. Well, he was defending only 20 percent of the time because he's making good plays out of our end. He may not be the strongest defender, but he's only doing it 20 percent of the time. So the equation works out better the other way. I ended up trading the other defenseman."
I've always loved Girardi, there is definitely nothing personal here, he seems like a great guy and you have to love it when an undrafted player becomes an all-star. But the more I've looked in to him this summer, the more I see an average player pushed to stardom by his superior peers (McDoangh, Staal and maybe most of all Lundqvist).