I'll preface this comment with this, Murphy has been decent, not complaining about him as a whole. The trade has been OK, we have lost it IMO, but it hasn't been a failure.
But this leaves out the HDCA for both players:
Hjalmarsson: 360
Murphy: 424
It also helps Murphy that this team creates A LOT more offense than Arizona does, so Arizona is playing in their own end more often than Murphy is. (not by much, but it helps Murphy slightly more). And Hjalmarsson also starts in the D zone more often (72%) compared to Murphy (65%).
Hjalmarsson is obviously the better Dman of the two, but he is right, it's not as bad as some people (ahem
@Blackhawks , and
@Blackhawkswincup) say it is.