I don't believe hits or blocks are good indicators of defensive prowess.
Not by themselves I guess.
But I believe hits are a major factor when it comes to disrupting a teams system and/or wearing key players down over the course of a game
So hits may be a part of a defensive strategy more then defending a play. I know the argument that hits take people out of position so it's likely a fine line.
Blocks? Well I'm almost certain that if purcell blocked a few shots he'd be a better defender. Maybe you mean he might score less and win less games that way.
Anyway, I get what you're saying but it's not like the stats are hiding the fact that he's a brilliant defender from watching games.